Let's see...10 years in the past I would have been 13, and a freshmen in high school. I guess if given the chance I would my young self these things:

Be more assertive- Like Violet, I was pretty much a pushover, too. I had really low self-esteem, so I thought it was easier to deal with if I just let people do whatever and not do anything about it. I'm still learning how to speak up for myself, but my first impulse when confronted is to cry. Yeah, I'm a crybaby.

Tell Robert that you like him- Probably the biggest crush I had ever had in my entire life. I found out later that he liked me, too, but he wasn't sure how to approach me, so he didn't tell me. I think he's married now, and I wish him a long and happy marriage.

Do more extracurricular activities- Looking back now, I wish I was a little more involved with the social aspect of school, and the clubs that my school had. I was too shy to do anything like that, so I stayed away. I focused on my studies, and I did well in school, but my college application would have looked 10 times better if I had done those extracurricular activities that my school offered. Scholarships would have been easier to get, too.

Hmm...that's all I can think of at the moment. I may come back and edit some more stuff in, because I'm sure there's a TON of stuff that I'm forgetting.