Help with this girl really like?

[Mark]

I'm 17, in sixth form, and there's this girl in some of my classes who I really like. Problem is, I hardly know her, as in, I never really speak to her. Like, ever. I have done a few times for group work or something, but we've never had a proper conversation, know each other by name pretty much and that's it. I can't just go up and talk to her, I'm kind of quite and I wouldn't know what to say. She's slways around her friends anyway, and there's no way I can go into a group of people I hardly know and talk to her. I even had a dream about her last night, wtf does even mean?! I usually end up staring at her in class and looking away quickly whenever she looks back. This is like a big movie clique but it's real life so I'm not gunna end up saving her dog and winning her heart or whatever.
The biggest step forward I have made is liking her fb profile picture. Jesus. There's so many other boys who she talks to as well so even if I did get to know her I doubt I'd have a chance.