Hair, eyes, smile, in that order. Studies show (and I can say from my own personal opinion) that guys really do notice a girl's face first. Give me a pretty face and I'll be all over her. I like a girl that knows how to be confident (the way she carries herself), but was taught good old-fashioned modesty. Also, if she gives me attention, then I'm more likely to notice her. I can't stand girls who treat others like they're better than everyone else. That's a huge turn-off, and it easily trumps a good body.
A nice smile, curly hair, a halo on top of her head. I also have a thing about hair being ginger and freckles, those are the two things that will get me interested. You get me a ginger girl with freckles and I will be like a dog with a bone. ;D
If she come across as different from most girls and it's not forced (Meaning, she's being herself) is the fastest way to get my attention. You can have a great body or look like some supermodel clone all you want; that alone will not make me notice you. It will just make ol' jimmy stand up...probably. If I find her attractive is an obvious one. I'm attracted to tomboys and punk/rock chicks. Cute tomboys more than anything. There are different from most girls.