Trust me if she's single she probably wants a boyfriend because all of her friends are pairing up, so to get her under your arm do this... so just look at her and smile ,be stupid,make her laugh then just tell her that you really like her...
look into her eyes and look away or keep smiling but before all this establish a good friendship! then start flirting... also walk with her in the hallways and tell her how your days going... help her with problem friends, family, homework, or even just picking up her dropped notebook will make her day... oh yeah and get a&f cologne it smells amazing.
This is all not going to work. do this: Make her your friend, become good friends, help with her problems, invite her to your house, ask your parents if they like her, if they say yes, continue, if they say no, DITCH HER, then ask her to go to the moivies (Choose a movie that is sacry. But not to scary) at the scary part, put your arm around her and if she likes it and she starts to cuddle with you, then try to kiss her, if she likes it the MAKE OUT(Make sure that you breath smells good. Then GET SOMETHING GOING!
Here's how you ask them out:
1. get to know them REALLY well
2. then text them "i love you"
3. When they're like "WHAT?"
4. Thats when you say "sorry! i meant to text that to my brother (or someone like that) and then say "but... do you like me? I think your really nice (this is safe because you dont "like" them you think they are pretty
5. if she says she likes you back... thats when you make your move