Ok, I'm actually gonna thunk for this one, JUST for you, man.
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Ok, you can go with what sasuke said and try small things, gradually getting bigger, like a hug, then maybe a small gift, then flowers, and so forth. That would be a good way, but her friends might try something (just knowing the people there). It's good as a careful way, if she's a dainty kind of girl.
Or if she's more aggressive (like that she plays a sport), then try a big show to really get her attention. In my experience, a girl that's aggressive (and I've had a lot of aggressive girlfriends) wants a man that's just the same, partly so that she can indentify with him, and also so that she can take a break from her "always in command" personality and have someone that's sensitive, but is bold enough that he's not afraid to show his feelings for her.
Or maybe try them both. Go slowly at first to let her know you're interested, then do something big to show your affection for her (song, drawing, poem, etc.) in front of her and her friends (if you can work up the nerve, if not, just her) to show that you're serious about it. It'll be a LOT harder for her to turn you down with her friends and other people watching.
It really depends on what kind of girls she is, or if she's a mixture, then use what you think would work best.
So now my brain hurts and cartoons are on, so no more thinking for now.
