Guys, I'm the same age so I know what you are talking about. Only too well. Thing is, every chick in HS tries to be different from group on one hand, but on the other hand she tries hard to fit in. With this in mind, knowing a lot of people (yes, you heard me, be popular) can be HUGE social proof. Also, in these years chicks are SUPER-HORNY, looking for guys to date. So, as soon as school starts, put on some good clothes (simply something NICE, that NO ONE ELSE wears - the best peacocking in school), get to know some chicks and RUN THE GAME! Do any opener you want - I personally find the ass grab too offensive, but whatever works out for you is fine for you. Maybe the best is simply HI!

I'd say know a lot of people, change the group you hang out on regular basis and you'll meet loads of girls. Get to know her in the evening (don't know about you, but local high-schoolers fill the city on friday and saturday evening). In school afterwards (that is, on Monday) bump into her "accidentally," small talk, and invitation for coffee after school (just to "chill out"). Best is to take her to café you go out regularly, knowing guys inside and name of the waiters is HUGE social proof.
Just have fun, hang out with lots of people and you'll get some pussy. And remember - most chicks are self-conscious in this age so watch out for over-negging.
Carpe Diem.