how to talk to my crush on fb ??? ladies advice pls (10pts)?

[Curtis]

I was in a class with a girl i found very attractive, the problem is we never talked to each other cus she sat in the front while i would sit in the back. Anyways, we knew each other's names by the teacher calling rolll..etc..any ways semester ended and I added her on FB a few months ago and chatted with her about class for a while, but it didn't go anywhere. I deleted my old fb, for personal reason, then created a new one about a month later...so i added her again, and she accepted again... It's been months since I talked to her and I want to try again...how many messages should i write before i ask her for her number or to hang out? and how would you do so?