We'd need some kind of reasoning behind why they wouldn't tell the person that they are the Avatar beyond simply because it would change their perspective. Perhaps there is some strife concerning the Avatar in the place they live; like the people there don't believe the Avatar is meant for good and instead believes that they are somehow evil due to their ability to be more than singularly elemental. Also, you'd have to describe to me what kind of characters you'd like to me to play and how they'd fit into the storyline in your eyes - such as whether or not you were looking for an adventure-type roleplay, an action-roleplay or something else?

Also, how do you want the world to respond to itself? How much violence are you willing to portray and how dark a personality will we be able to find? What do you think of bloodshed? Will there be an enemy the Avatar should be facing? How old is the Avatar? What kind of history will that person have with bending in general?