Could you give me ideas on how to approach her?

There is this girl I want to get to know much better. I have a little crush you could say. Problem is that she is a freshman and I am a junior. We do not play any of the same sports, and we have no classes together, nor do we really have any mutual friends, we are only friends on facebook ha. So if you could just fill me in on some ways to maybe approach her? How to get her cell phone number etc. and begin to speak to her more to at least spark a friendship.