Ah, childhood! I love this question...
Dear Claire-Bear,
It's me! I mean, it's you! From the future! Crazy, right? :) I get to write you a letter telling you the things I know now at 25. So here is my sage advice to you, little girl.
1) It doesn't pay to be popular.
Somewhere around the end of your sophomore year of high school, you'll get this idea in your head that you need to hang out with the popular older kids. You'll be pretty successful at this...but it gets you into trouble. Your grades drop, you're dating someone you don't even like, and it's just bad news. AVOID THIS IF YOU CAN! It's SO not worth it. You'll have to get back on track the end of junior year to get those grade up for college acceptance and your old crew will leave you anyway. Bummer. Don't do that, darling.
2) Move away from home for college! Go to a big city. Explore. Work hard. See art. Be curious. You're going to find what you're looking for. And yes, you'll miss your parents. But it's okay. Technology is way advanced and so it'll be super easy to stay in touch :)
3) Enjoy being 10. You are so silly and wonderful. Don't worry, you'll make mistakes no matter what I tell you now, but it all turns out alright (especially at 25 - things are great!)