Creative writing is a good class to take, if your school offers it. Speech, or public speaking is also very good for someone that wants to direct, and wants to be able to sell their work to studios/producers. Art classes don't hurt either. If you can make your own storyboards, it's a very convenient skill to have.
You should order a couple of screenwriting books. Or go to the library, I'm sure they have some. Just to help you learn proper format. However, if you're going to write/direct, then you can even do it without a properly formatted screenplay.
Just do what you can with your camera now. And make sure you keep your grades up in school so that you can have a good shot at getting into a film school after you graduate.