Document you for the future.
When you're older, it will be fascinating to look back at the "you" you were over the years. Start now to create something that shows who you are now. Some girls like to make time capsules. You could include items such as photos, favorite music, a letter you write about you for your older self, small things you particularly like, or whatever says something about you. Put it in a sturdy box, seal, and decide when you'll open it.
Another easy way to document yourself is to write a letter to yourself each year about your thoughts and passions, and tuck it away until you'll read them as a grown-up. Diaries are great--you can keep one on paper or on the computer.
Diaries don't have to mean writing every day; you can write as little or as much as you want.
Whatever you write, don't ever throw your writings away, even if re-reading them makes you judge your old self as dorky or uncool. If you toss them, you'll regret it as an adult, because then you won't have an honest record of who you were.
One easy "time capsule" to make is simply taking the "What Will You Do?" survey at NewMoon.com. Save your answers and read them again in five years or 20 years!