Help...what should i do with this girl?

There is a girl in my grade(high school) and i've seen her for the whole year but never got a chance to talk to her. I don't know who she hangs out with and know nothing about her. I really want to get to know her and maybe ask her out but don't know what to do or how to approach. Shes really quiet and nice personality from what i've seen from afar.