Contrary to what Daniel-san is saying, picking up chicks in class is not easy. I haven't had any luck. Though that is usually because I wait too long to ask girls out.
An easy topic is asking what she did over the weekend. You can also use that conversation to find out what her interests are. A clever line to use in the conversation is a variant of, "Did you go there with you boyfriend?" She will give you one of three answers. "Yes I went with him", "No I didn't go with him", "I don't have a boyfriend."
In that one conversation you can find out what her interests are and if she's single. If she isn't single it's for you to decide if it's worth the effort to steal her.
The real challenge is finding out what to do from there.