Replying to How to talk to girls

So recently Ive been hanging out with a few guys and girls at school and occasionally outside of school and Im interested in one the girls and she seems like she possibly is to. The problem is I am shit with girls and most people who Im not close with for that matter, I want to start hanging out with her over the summer but Im very awkward, what do I talk about? All I talk about with friends is usually cars or skiing. Help me NS