'Oh I'm the chosen one!"

Don't get me wrong, there is nothing wrong with the use of the 'chosen one' plot device, while it can be cliche, set up correctly it can be used as a great coming of age story (unforgivably that's all I find it's really good for). It can become wrong quickly however when it is used in a manner that is not plot driving at all or in an abusive manner. The chosen one case is where an oc is the special, the 'one' who can beat an evil that sets out to destroy all, solve a problem seemingly nobody else can solve, stop corruption, etc. Basically, they are the only person who can save the day. Not their sidekick(s). Not Mom. Not Dan. Only them. Typically a order of 'the chosen one' comes with a side of a prophecy, a message from some higher power like a god or goddess.

Where this becomes sue or stu is when the character does something along the lines of these three things;

One- The character knows right away that they are the special. Nothing is more boring than this. I'll use an example from the Beginners story i'll be writing soon about how I believe the Starwarrior Army started. Balhfire, named Percival by the human who raised him is NOVA's second Star Child, a child born when a force of darkness is growing powerful enough to destroy the universe, this threat of course was NME. He was sent to make sure that the GSA started after the events of Galatra's Paradox nearly eliminated all of the starwarriors, and if someone didn't bring them together all would be lost as nobody could fight the Dark Empire. Blahfire never believed himself to be special, he even goes his entire life (only when his task is complete and NOVA calls him back does he learn his purpose) without knowing he is this chosen one. I see too many characters with the 'chosen one' who will shove it in others faces that they are special and than other the other story characters woo over them and worship them instantly. These removes the sense of challenge and destroys the meaning behind any friendship the character makes, as we know the other loves the chosen without a doubt and is unquestionably loyal. 

 Two- Because they are the chosen one, suddenly they have powers that 'nobody has ever dreamed to be possible.'  This is more of an iffy, as some chosen one's powers are needed to preform the task they were chosen for, like Kirby who had to be strong to defeat NME. That being said, if your chosen is going to have special powers, do not have them instantly understand these powers or have them immediately able to use them with much skill. The idea is to have people root your OC on, if that OC is powerful it becomes obvious they'll win no matter what, which of course is rather boring and of course annoying.

Three- If there is a prophecy, it's super easy to understand yet everyone pretends it isn't and or it instantly lets anyone know who the chosen one is.  Most chosen ones come with a side of prophecy, this is given to them by a god, goddess, or person with connections and or ability to see these prophecies. Now I'm not saying all prophecies have to be over complicated master pieces, simple prophecies can work as well. Kirby's prophecy, "A puffball (piyan) child born of both the sides of light and darkness will rise up and defeat the lord of darkness NME, ending his rain forever," was given many, many years before Kirby's birth. As it was never time specified, this lead to a few thinking they were that chosen one. First some thought Percival was that chosen one due to having a wing of feathers (light) and a demon's wing (dark) although he denied such and it turned out that indeed, he was not the child. When Arthur and Meta Knight were born, Kele specifically thought that it was Meta or Arthur, which resulted in their names. Arthur was named after a great hero of the same name, as Kele believed he too might be a hero, and Meta's name meant to change and go beyond, where he would change the world by defeating NME. Like Percival neither were this chosen one, and it was years later when Meta Knight met Kirby did he realize that he was that starchild meant to defeat NME, and he helped Kirby become strong. Prophecies are well known for being extremely non-specified, they don't give a direct answer and leave many questions, I'd probably write a separate chapter on prophecies to explain them in greater detail.

The bottom line is that the use of 'the chosen one' is a coming of age story plot device, your 'chosen one' should start out weak and inexperienced, if he or she is told about them being a chosen one it should be incredibly shocking and unbelievable news to them. They should react like they've just grown a new arm and that's not normal. They could feel all mighty and invincible for a bit, but they should learn quickly that being the chosen one is an incredibly difficult task that several times should knock them down heftily, made them and others doubt them, and in the end make them grow as a person and reach a goal through extensive struggle. Remember the chosen one is fighting against something, so not everyone will like them and they will have enemies that want to stop them, and keep in mind to have those who don't believe in prophecies and are sceptical of their existence. A good way to make a chosen one is to make a character bio and pretend for a brief moment they are not the chosen one, clearly define their personality and powers, than add the chosen one on top and try to stay true to the character's personality. Like immortality, the use of the chosen one should match up with a character's history (like perhaps their culture) and their motives.