Can you give me some advice?

I'm just to like this guy. He is taller than me and he plays football and baseball. We don't go to the same school, and we got introduce to each other by our moms. And I kow he likes me to. But every time we talk I never know what to say. I don't really have any boy expeirence at all. What should I do the next time we talk or see each other? because he did ask me out, but I coudn't go out with him because of my grades. Can you help me.