This question was asked of me when I was in college, ages ago, and at the time, it didn't really click with me until I really started to get into novel writing.
To start this off, my characters are just like normal teenagers. Boring right? Well it would be except that being normal everyday teenagers requires intense focus because otherwise they could literally destroy everyone they know.
For example, Rebecca in my current story went to a school dance once, but because of her telekinesis, she had to leave early when her nemesis Gretchen stole her date. Now she could have threw the poor girl through the wall, but that would have put a damper on her very small social life, so she had storm away before her own energy burst from her.
So what sort of things do your characters do when they aren't in your story? It's small things like this that affect your characters decisions when they arise in your book, so what are some of more interesting tidbits, not like my example was the best.