Well I was looking at the Floris Wiki and noticed the "Advice For a Liege" section was blank under the New Player section. Considering becoming a King is, in my opinion, one of the greatest aspects of Mount and Blade I figured I'd do a quick little write up on how to be a successful King.

Starting Up
It is always best to decide what you want to accomplish in a playthrough before starting said playthrough. Having a set path to follow ahead of time saves you from making errors or skilling things you won't actually need. Like if you put points into Power Draw but never actually use a bow. Those points could have been better invested elsewhere and while it probably isn't game breaking, it is a hindrance and annoying to find out you upped something you didn't need.

The ideal type of character for becoming a King is built around your character being a decent fighter, a maxed trainer, a maxed surgeon and as high of leadership as possible without investing into Charisma. As such to start off your game you'll want to select the following options....

Male or Female - An Impoverished Noble - A Noble in Training - A Troubadour - Sense of Duty

The most notable things this setup gives you are...
+6 Leadership - Which with a book will make it +7 without you having to invest anything into Charisma.
+115 renown - Which makes your early game generally easier for joining a faction or being a mercenary for one.

Other skills worth mentioning are...
+1 Power Strike, +2 Weapon Master, +2 Riding, +2 Tactics, +1 Path-Finding, +2 Persuasion - All of these skills are directly beneficial for a leader type of main character.

Starting stats are - 7 Strength, 6 Agility, 7 Intelligence, 10 Charisma

Once your character is setup you come to the character page screen which gives you 4 attribute points and 7 skill points to use for boosting your character even further at level 1. I suggest placing them as follows...

Str 7 + 4 (Place all 4 here)
Agi 6
Int 7
Cha 10

In terms of skills you'll want to maximize your combat potential early on to help level up quicker...

Ironflesh 0 + 3 (For more HP)
Power strike 1 + 2 (For more Damage)
Shield 0 + 1 (To equip a basic shield)
Prisoner Management 0 + 1 (Good for making a little more money)

All of your proficiency points will go into the weapon type of your choice, pump it always until you can't up it anymore. Personally I'd suggest doing a 1 handed weapon.

Early Game (Levels 1 through 15)
This is probably the most challenging part of the game as you'll need to avoid most major battles and focus on just killing Looters for a while. Once you get some troops and some levels you can try to take down other bandit/deserter packs, just don't bite off more than you can chew. If you see battles taking place, always hop in and try to help one of the sides. Keep your men on hold position so they don't die and run around with the other people's troops and pick off enemies where you can for easy experience.

Where you start isn't relevant, you'll want to do the initial quest line and save the merchant's brother then help them rebel in the town. This nets you some early experience, money and a few troops. From there I suggest taking a trip around the world visiting every major town on the map. You'll want to avoid tournaments for now as they are probably too hard, but your goal here is to level up via bandit fights as often as possible and collecting companions. On top of all of this you'll want to do quests for Lords, Guild Masters and Villages as often as possible. I suggest only doing the quests for the area you plan on starting your kingdom. The best places for each faction are...

Nords - Wercheg (Due to its isolated area, unlikely Nords will move over there often to try retaking it)
Rhodocks - Yalen (4 villages connected to it, secluded and has a couple castles in choke points to take after)
Swadians - Praven (Swadians are typically at war with multiple factions at once and get crushed, so you can take advantage of that and pick it off)
Vegirs - Rivacheg (Secluded)
Khergits - Halmar (Far away from their other towns/castles)
Sarrinids - Bariyye (Same)

As for the companions you'll be looking to recruit you must decide ahead of time which groups you'd like to use as not all companions get along with one another.

Standard 11 (Credit goes to eastpaw for this setup)
If you want to have a party that never complains about one another, pick up to 11 members from the following:

Once you have your 11 companions picked out, you'll want to wander around until you find all 11 of them. If you run into a companion not on your list then recruit them if you have the spare money. You'll then want to talk to them and send them off to support your claim to the throne. This will start to slowly increase your Right to Rule, which is essential for any king. You can only send one companion at a time to do this, so once they get back if they aren't part of your standard 11 just remove them from your group.

This is pretty much all you do for the Early Game stage, you're going around setting yourself up to be a successful King later on. These are the stats/skills you'll be aiming for by level 15...

Attributes
Level 15 (14 attribute points available)
Str : 11 +1 = 12
Agi : 6 +6 = 12
Int : 7 +7 = 14
Cha : 10

Skills (21 skill points available)
Ironflesh 3 +1 = 4
Power Strike 3 +1 = 4
Weapon Master 2 +2 = 4
Shield 1 +3 = 4
Riding 2 +2 = 4
Athletics 0 +4 = 4
Trainer 0 +4 = 4
Tactics 2
Path-Finding 1
Surgery 0 +4 = 4
Persuasion 2
Prisoner Management 1
Leadership 6

Mid Game (Levels 15 through 30)
Now that you're a decent fighter and on your way to becoming a solid King you should now become a mercenary for a faction, preferably the one you plan on starting your kingdom in. You don't want to help them become too strong, but you'll want to help in all sieges and lord battles to see for boosted relations and easy experience. The mid stage of the game is the most important part for setting yourself up to rule a kingdom. You'll be making money, building relations, increasing honor/renown/RoR and leveling up.

Making Money :
Prisoner Selling (If you use 40+ manhunters you get a +3 bonus to prisoner management and they help you make lots of money)
Buying land (A huge money sink but after a while the money gained from it becomes pure profit)
Building an enterprise (This can be done in every major town you have a positive relation with its Lord in, gives a weekly income like owning a villages/castle/town)
Winning tournaments (Careful as they're quite difficult)
Plundering villages (Only plunder villages of enemies, not randomly, to avoid losing honor)
Selling loot you find from fighting.

Building Relations :
Town Relations (This is upped by winning tournaments, buying rounds in the tavern and doing Guild Master quests. The higher the town relation the better prices you get for buying/selling in that town, which goes for your Land and Enterprises as well. You'll want to aim for 25+ relations in every town near your starting area.)
Village Relations (This is upped by clearing out bandits and doing quests for the villages. The higher your relations the more recruits you can get from the villages. Suggest 30+ relations with each village in the area you're going to be recruiting most of your units in.)
Lord Relations (Helping Lords in battle, doing quests for lords, freeing lords from the enemy and letting prisoners go all increase relations.)

Increasing Honor/Renown/Right to Rule :
Honor (Letting Lord prisoners go after a battle, certain quests and not taking rewards after helping villagers all increase honor. Once at a high enough point other honorable lords will start to like you more over time.)
Renown (Winning tournaments, fighting in general and certain quests increase renown. The higher your renown the bigger your overall army gets to be.)
Right to Rule (Sending out companions on the missions, if you become a Lord for a current King temporarily whenever they go to peace you gain RoR and getting married to a noble family member. You'll want about 75 RoR before you start your own Kingdom, if its too low once you start it everyone will try to war you to get rid of you.)

Leveling Up :
Continue doing the same thing you've been doing. Remember your units are expendable, you will be making LOTS more as your time goes on. So even if a fight looks like you'll take heavy losses, do it for your main character's leveling.

That covers the mid stage of the game, you'll likely be around day 250+ when you reach this stage. It seems like a long time, and really it is but setting up your stage to become a King and rule the world is not an easy task. These type of playthroughs typically take up to 1k+ days to completely win, however winning one is the most rewarding feeling M&B has to offer in my opinion. Your level 30 stats will be as follows...

Attributes
Level 30 (14 attribute points available)
Str : 12 +1 = 13
Agi : 12
Int : 14 +13 = 27 (You'll never want more than 27 int as this gives you level 9 in the skills and a book will give level 10)
Cha : 10

Skills (26 skill points available)
Ironflesh 4
Power Strike 4
Weapon Master 4
Shield 4
Riding 4
Athletics 4
Trainer 4 +5 = 9 +1 from book = 10
Tactics 2
Path-Finding 1 +8 = 9 +1 from book = 10
Surgery 4 +5 = 9 +1 from book = 10
Persuasion 2 +7 = 9 +1 from book = 10
Prisoner Management 1 +1 = 2
Leadership 6 +1 from book = 7

Late Game (Level 30+)
Its time for all of that hard work and preparation to pay off. Finish getting +30 relations in atleast 10 villages, +20 relations in the 5 nearest towns, enterprises in every town, 20+ land in every town and as much relations with lords as possible. You'll also want to stock up about 50k denars before starting your kingdom for emergency use as you'll find yourself needing to resupply ALOT of troops very quickly. Once you're all set, get your army ready and move towards the town you're aiming to take. You'll always want to start your kingdom with a Town and not a castle. This is due to the number of villages connected to it and how much more money you make from them. The more villages connected the more Lords you can convince to join you right off the bat or the more Companions you can make into Lords. Either way works.

The best starting location is Yalen due to its secluded area and 4 connected villages and for the means of this guide we'll use it for the example. This means right after you take Yalen you can try to get 4 Lords to join your cause or make 4 of your companions Lords. Once you take Yalen (it won't be an easy fight) you'll want to get it stocked with as many troops as possible because the Rhodocks are going to be pissed and will be coming at you with thousands of troops. It is best to wait until they are at war with 1 or 2 other factions before doing this so they aren't as organized against you. Also note that low tier units are your best friend here. A 1k+ troop garrison in your starting town of tier 1 through tier 4 troops will keep most lords away from you. You'll want to sit in your town with your 4 lords following you and have the recruiters going out (you get 4 of them) finding you troops. With your high village relations they should be bringing back 200 troops to you every couple of days.

You're basically just waiting for the first attack group to come, and they will always come. If you survive that and manage to take the enemy king as a prisoner you can sue for peace. If you fail to defend it then dust yourself off and retake Yalen to try again. If you succeed in defending it but fail to capture the king then odds are in another week or two you'll be attacked again. During this time DO NOT try to take other castles and such yet because the attack will come again. Essentially you're looking to defend until you capture their King and force a peace. You cannot take on a faction alone this early on in your rule.

Once you get a peace going you'll be working on building up your 4 lord's parties. You'll recruit troops and place them into their groups which will greatly bolster their numbers. Once those 4 lords have about 300-400 troops each you'll then go to war again and pick off castles and such. With your first castle you'll want to give it to one of your current lords, not get new ones to join you. This is so they'll have bigger armies normally. Once those initial 4 lords have atleast 2 villages each or 1 village and 1 castle, then you start trying to get more lords to join your cause.

From here its basically just taking, defending, losing, retaking, ect until you rule the whole world.

Things to be aware of while king...
-Everytime you give a fief to another lord, every other lord will decrease in relation with you by 1. This is unavoidable. To counter this hold feasts often, help them in battles and give them troops. This will keep them in good relations with you.

-Being a king is expensive, lucky for you though you prepared ahead of time with all of that land buying and enterprises.

-You're going to lose castles/towns, its inevitable. Don't be discouraged and just retake them when possible.

-As you level up past 30 you'll want to boost your combat skills more, so pump your Strength and Agility. You'll never need more than 27 Intelligence. Don't worry about Charisma as your renown will get you larger armies.

-Try to avoid going to war with more than 1 faction at a time, if another one declares on you while you're waring someone else sue for peace with one of them as quickly as possible. You never want to fight on two fronts at once.

That about sums things up. For things like how to build companions and such, that is up to you. I suggest having several of them be trainers for rebuilding armies. Aside from that hopefully this guide proves helpful and you succeed in your conquest to rule the world!

Personal Companion Choices
Artimmener - Engineer/Tactics
Borcha - Path-finding, Spotting, Tracking
Lezalit - Trainer/Combat
Matheld - Looting
Rolf - Trainer/Combat
Alayen - Persuasion
Klethi - Foraging
Ymira - Wound Treatment, Surgery, First Aid
Baheshtur - Trainer/Combat
Firentis - Trainer/Combat
Nadia - Trainer/Combat

Diplomacy
Figured I'd add this little tid-bit into the guide as well as it is quite important. When you're a King you have the ability to send emissaries to other Lords and Kings. The person you send is always a companion, you want them to be a Male, Noble and have a high Persuasion skill. Lords and Kings are picky and don't want to talk to commoners, women or people with low persuasion when it comes to matters of diplomacy. Yeah that's pretty messed up but hey that is how it works. This is why Alayen is chosen for the Emissary if you follow my "Personal Companion Choices" as he fits all of the requirements.

War/Peace/Trade-Agreements/Alliances/Pacts
War : Obviously when you declare war on another faction you guys fight until only one remains or peace is sued for.

Peace : You can sue for peace usually when the other faction is at war with multiple factions, you capture their king or you're just stomping the crap out of them. You might ask, why sue for peace if you're winning? Well if another faction declares war on you while you're stomping the first faction then you'll be fighting 2 wars which is very bad.

Trade-Agreements : I've never actually made one of these but I'll assume it increases the amount of money your towns and such make from caravans and such.

Alliances : Never done this one either but I'm pretty sure you just end up at war with whomever they are fighting and vice versa.

Pacts : These treaties can be make after a war to guarantee you guys won't fight again until the end of the pact. The player can break the pact and attack early but everyone else gets pissed at them for doing it.

This is an awesome and well-detailed guide! I'd like to add an addendum about some things, if it helps: 

Village Management:
After becoming King to a city, one of your priorities is to build even better relations with your connected villages. Hire a treasurer, and lower all the village taxes down to Very Low. Don't bother lowering the taxes on the city, unless the economy is suffering.
This will do two things: First, Very Low taxes will increase relations every week. Second: It will help improve the prosperity, especially if said village has been sacked many times.
Very high village relations and prosperity will yield massive amounts of recruits. I've recorded getting about 170 T1 and T2 troops on a single recruit, and about 50 T5 on another, on a 99 relation village.

Also remember that you can now swap fiefs with another lord, so when one village hits 50+ relations, swap with a lord who has a low relations village, lower taxes, and profit!

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Leaving an Open Village
This is something you need to address when you conquer your first property outside of your capitol. Whenever a new castle or town, always select to appoint someone in the future.

This has several benefits:
-You can discuss with other lords as to who gets the fief. If you have high persuasion, you can convince them to support your choice and not suffer the relations hit you would normally get. Plus, if you speak to your adviser about how the other lords are feeling, you can gauge which lord likes whom (which helps, because you actually get relations boosts if you grant fiefs to lords whom have friends or relatives).
-You can choose to leave the satellite village unclaimed. You will miss out on taxes and relations, but every lord with decent relations and a grudge against their boss will come knocking on your door.
This leads to...

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Selecting Your Lords
During your travels, make sure you introduce yourself to every lord you come across. This is because it adds them to the Known Lord List, which lets you see their renown, personality, holdings, and feelings towards their liege. This is invaluable when you start to preemptively headhunt personnel for your empire. Lords with negative relations to their liege will be able to be convinced to your cause, the lower the better chance. However, you always need to use the SAME pitch when you persuade them, or in the future, people will call you out on your flip-flop.

Obviously, you are going to want lords with high renown, but even a low renown lord with a village can help you out in a fight, so don't discount them either (but don't go around giving them your most important castles and towns!), but more important is their personality. Personality can make or break your kingdom, as having very divisive lords will tear your kingdom apart with arguments. I'll break them down as so:

Do Not Want tier personalities:
-Bad-Tempered/Quarrelsome: They're basically jerks. They do not get along with anyone other than their relatives, and will cause massive amounts of tension and arguments within the kingdom, that you will have to take the time out and solve. These guys tend not to stay with their kingdoms for too long.
-Debauched: They will want to screw anything that moves, which leads to many, many fights over women. Not as bad as Bad-Tempered, but it's very much a pain to deal with, unless the lord was too good to pass up.

Managable personalities:
-Martial: This is one of the more preferred personality types to work with, as most lords in the game have this one. Easy to manage and get along with, as long as you give them a fief to work with.

Not Sure, but I avoid anyways:
-Pitiless/Sadistic: (I avoid these types, but if anyone wants to fill info in, it's appreciated!)
-Calculating/Cunning:

Desirable personalities:
Upstanding/Good-natured: The best guys, hands down. Their relations with you will go up as you get honor, AND they do not lose relations with you. There however is a catch: They most likely have absurd relations with their lord, and will never ever leave him. However, there are times when the planets will align, and a U/GN lord will have bad liege relations: GO AFTER THEM! If you're at war, fight them as much as possible and imprison them. If you're honorable, you probably already have good relations with them, and each time you defeat them, they lose relation with their liege.

As for guys that show up on your doorstep: You will not have a way to see their personality until you recruit them, so just save, check their personality via the chancellor, then reload if the guy is not to your liking. For those who are on realistic mode: Simply don't give them a fief, and never side with them. They'll go away eventually.

Granting Fiefs

As I mentioned earlier, remember to discuss with the other lords and try to convince them to your motives. But also remember that lords will patrol the areas around and between their fiefs. So give important chokepoints to powerful and high-renown lords, and keep appointed fiefs close together, so they can rush to their defense when they are sacked.