i asked a girl out over aim once for shits and giggles, it worked but now every time i think about it i wanna kick myself in the nuts. do it face to face, any other method and you seem like a nervous pussy. just ask her if she wants to go out some time, maybe a movie or go to your house and flex your skis while she sits bored on your bed.....
just be cool and if she likes you and is chill, she'll say yes, if she's not ready, she won't beat you down she'll just come up with some way to say no in a nice way, girls are good at that, they never flat out reject you unless they don't know you or hate you for some reason. if you're getting a connection, it'll all work out fine. just don't say something totally retarded, i was talking to this chick once and we were talking about girls with short hair and i said i thought they looked weird and she was like "my mom had short hair......she died of cancer." we sat awkwardly for like 10 mins and i wanted to kill myself