Hmmm... high school and you want girls comfortable around you...

Well if I could go back in time, I would: Stop hanging out with groups of guys. Start hanging out with groups of girls or one or two girls at a time. If they reject you, prefer to be alone. Don't hang out with the guys.

Don't try to look cool to other guys, and don't seek their approval with how you dress, act, where you go, etc. Remember, you're not attracted to THEM! Don't care what guys think if you are rejected by girls or groups of them. Remember, you're the one who's ultimately going to have the success and they're not because they're too chicken shit to try. If the guys think you're a loser, then you're probably onto something good. Just ignore. They will probably try to reject you if they see you breaking out of the norm. These things do not matter, you want to be different from them.

Just focus your time on meeting all of the girls and being around them. They will be comfortable with you when you are comfortable with them.

Hm... If you're the guy you should be in control. If she's quiet it's most likely because you are. The energy is your responsibility. This is why the girls you are friends with seem more fun and outgoing, because you're not afraid to be the same way around them and they feed off it.

On the same note, treating someone like you're already close has a shocking ability to affect their mindset and actually make them feel close to you.

@Origami
The foundation of your advice is good but you need to be careful here. I was a worse than AFC in my highschool days. I was friends with almost every girl in my class and one above and below, but only had 4 or 5 good guy friends. All the girls thought I was cute, only the creepy/dirty ones wanted to date me.

Remember, women want men of high status, and social proof (already a big deal) is blown wildly out of proportion by the highschool mindset. The girls aren't drooling over the guy that's talking to them about their feelings. Their drooling about the guy that they see all the other guys high-fiving. The guy who probably doesn't even know their name.

girls being comfortable around u isnt always a good thing this u need to be careful of, ive always been told by friends and strangers i meet they can trust me really easily which is good however if not watched like when i was younger before i started properly gaming this trust stuck me slap bang in the friend zone before the 7 hr window had even passed lol

Charlatan:
Good info. Social proof is important in high school I would think, though I think who you are "friends" with is important too. In high school you don't want the girls to think you tell all the other guys who you've slept with, so it's debatable there.

I'd like to add: I think my biggest mistake in high school was attaching too much meaning to one girl's response. I think I asked out one single girl in high school, and when she said "no", I never asked another one. I thought it really meant something (unconsciously of course). Whereas today, I know it would not necessarily mean anything at all. You could ask 4 ugly girls and a cute one, and the cute one could actually be the only one who says "yes".
Social proof is definitely important, and I think social proof from other hot girls is definitely way more important than social proof from guys, although it could help a bit, as long as they are "popular" guys.