If Mumsnetters were writing a book of advice for teen girls (age 13 up) and you were asked for your contribution, what would it be?
So. for example, my advice would be:
Don't mess about at school. Study hard. Learn as much as you can about everything you can. Read a lot and read widely. Forget about boys and trying to find a boyfriend - boys will still be there in a few years time and you'll be in a better place to deal with them. Just concentrate on yourself and what's best for you and your future.
(Inspired by GonzoParker's thread: How do you internally validate yourself rather then getting external validation)