In most roleplays, there are certain guidelines you must follow. These are the three basic rules most roleplayers respect and follow.

PTK: Permission to Kill

You must have the consent of the owner of the OC before you can kill them. If not, people would just kill everyone they didn't like. There are a few exceptions - characters that would die if the beating they took is deadly enough. This means someone getting slashed and stabbed to bits as they were fighting (not someone of equal power - they will usually fight them off). Sometimes a ref (usually the owner of the RP) is called in to decide if they should die or not.

No Godmodding

Godmodding is when a character is too unstoppable and strong, without the consent of the author or other RPers. This includes killing, fighting dozens of opponents without any injury, or simply doing something that's physically impossible for your character to do.

Hate the Character, Not the Owner

Even when you don't agree with the character, you shouldn't hate on the owner of the OC for it. My OC, Ezra, is a womanizer and, well, a jerk. I'm sure a lot of people don't agree with his personality and his... ways. But they don't hate on me for it. They can separate the character from the owner.

There we go. Now you have the basics. There are other rules the author may request - censor/no cursing, censor/no smut, don't be in multiple places at once, etc. But these three are the big ones.

Next, I'll explain the several different RP styles.