How to escalate with a shy girl?

We've known each other for a couple years, but we haven't really talked until recently. We were in the same class a couple years ago and she laughed at most things I said, but since then we haven't interacted because, even though she's very good-looking, she hangs around her friends, even at parties, and doesn't really go around and talk to people.

But we're in the same class again and recently, she's made side comments to me occasionally/walked around me and then a couple days ago, we had our first real conversation and I had her laughing a lot. Plus I said something which surely made her know I was hitting on her.

She's shy, though, and I have no idea how to go about escalating things.
How to escalate with a shy girl?
Post Opinion