He is tall, but not too tall. Tall enough to rest his chin on the head of his love interest. He is thin, too, and a bit muscular, but not too fit. It can’t look like he goes to the gym everyday for several hours, although lets be honest, he probably does.
He usually has brown, or black hair. Dark and mysterious. But obviously, not too dark, or too mysterious. Your reader has to connect with him, after all.
He’s good enough at school. He misses way too many classes, because who has time for Math when you’re busy saving the world?
He’s pretty perfect. Chiseled jaw, just the right amount of stubble, 20/20 vision.
Actually, he shouldn’t be totally perfect. He has some “flaws” too, like his crooked grin. Make sure your love interest mentions it, oh, at least twenty or so times. If you want to spice things up a bit more, give him weird coloured eyes too. Lavender, amber, silver, emerald green, or even mismatched ones will do the trick.
Now all he needs is a totally overpowered super power, a goofy sidekick, and a decent amount of teen angst, and he will be ready to run off and save the world.
With little to no mistakes made, of course.