It's all psychological, man, so you have to play the mind games with her.
Be sure to befriend her friends since she'll be asking them what they think of you, so you want to be in their good graces. Besides, if she turns you down, you might have a few girls who like you since you got to know them in preparation for getting to know her. While doing all this, be yourself; there's no sense in trying to be something that you're not because they'll see right through that whole illusion. Also, stuff like proper eye contact, body language, and
conversation topics matter; they can tell a lot more about you than you might think. First impressions matter a ton; it's pretty tough to change them, so hopefully you're already on good terms with her.
Ever watch the movie "Hitch?" While it does not contain all good advice, there are some really good tips contained within the movie; you just have to pick up on which tips are good and which are bad. That's some advice that came from "America's Real-Life Hitch,"
David Coleman. As cheesy as this sounds, both the movie and Coleman have some pretty good advice that will work if you use said advice in conjunction with being yourself.
What kind of time frame are you looking here at anyway?