I tend to write the lead character as an underdog turned hero - or, in fan fiction's case, Nick. In my stories, Nick is always the underdog, the one no one expects to win... for example, the entire premise of Saving the Day for Blondes is that the other Boys don't believe in Nick, but he ends up being the one they all rely on. I guess it's Cinderella-syndrome! Even in The Time Watcher, Nick is a hero only because he is forced into it by "what he is" - making him a reluctant hero. There's a major part of the plot coming up soon that will test Nick's motives and goals with the ability he's been given. Nick is always pushed to the limits and forced to discover that he can be the hero, despite everyone else's reluctance to believe in him.
I also tend to make AJ be the very sexually-focused character. If anyone's gonna make a sex joke, it's gonna be AJ! And the others will only make similar jokes when it is purposely done in an out-of-character way.
I have issues writing 3-dimensional girls, too, for some reason. So most of my stories tend to focus on the relationships between the guys themselves - friendships being tested, tried, and found to be made of steel.