How do i gain confidence?

I want to know how to gain confidence. Im in high school && the guy that i like is as well. Anyway, I know his sister, and yeah we're friends. However, i really like him. Like alot! My only problem is that i dont have confidence. I know what to say but i dont know how. The problem is my approach. Please help. Im trying && I just want to be able to talk to him more without getting shocked && later be able to tell him what i really feel. Thanks(: