In high school I find that just going up to a girl and saying hi works pretty well. What you see in the Pick Up Artist, read in books, those are women that are 20+ years old, they've been approached thousands of times. Plus, most of the hot ones most likely go clubbing, and clubbing increases a girl's approach count by like 10x. In high school, barring a fake ID or hook ups from club owners the only dances these girls have went to are school dances. So opinion openers won't be necessary, however they'll still work.
Just appear confident when you're approaching her, maintain strong eye contact with your target. I remember when Style was going through this approach with one of his students in his program The Annihilation Method, he approached her with his hands in his pockets, back slanted and his head down. There's no way in hell this guy was getting anything out of that approach.