Alright here are the guidelines young grasshoppa, follow my advice and you will soon be mongoose.
Compliment her. Not on a body feature "Gee you have big knockers" does not work. PAY ATTENTION TO DETAIL. If you see her in clothes she has not worn before be sure to say "Is that shirt new? It looks great on you!" or "Your hair looks really pretty like that!". Remember to make sure these things are true.
Ok, conversation time. Guys are naturally systemizers, conversations cover cars, games, traffic, sports. Girls are empathizers, conversations revolve around people, culture, relationships. So what do you do? Ask her about her friends, be sure to say nice things about them but not too nice. You want to instill a bit of jealousy in the girl. Ask her what she thinks about a celebrity, if she dislikes them, agree with her, if she likes them agree with her, and remember to say why on both counts. Occaisionally when you have strong feelings about a person she is saying bad things about, admit that they possess whatever quality she does not like, say that they also can be X. Where X is something good about them. Avoid asking her about people who she is very angry at, the anger will project on to you.
Ok, now it is time to heat things up. You gotta make her feel that you like her without her KNOWING that you like her. Now you make your compliments more sexual. "You look really hot in that skirt! You should wear them more often!". "You're hair looks really beautiful". Use these only after establishing a certain closeness or she will feel like you are coming on to her. Then ooh... this is viscious. Don't talk to her very much for around 3 days.
She will miss you.
She will want you to talk to her.
She will start thinking about why you aren't talking to her.
Was she only imagining your interest?
Why does she miss you so much... does she like you?
Then, wait a bit longer, and suddenly talk to her like things are all normal again, don't explain, just pretend nothing was different and act confused if she says that you were avoiding her.
i'll give more advice later.