How do you talk to a girl who you don't have much in common with?

One thing that usually works when talking to people in general is to ask questions, and find out more about them. In learning more about anyone, we might discover things that we have in common, and even if not, we will find things that are interesting and that we want to know more about. And people usually like it when you show an interest in them, so questions are usually a good place to start. Be careful that the questions aren't too personal, and try not to ask anything too selfish, like "do you like me" or something. The goal is to find out more about the other person, not to find excuses to talk about ourselves. :)