Does your school have AP courses? I didn't realize you hadn't graduated already. Take as many math courses as possible... the same with english, science, etc. Don't take those lame "filler" classes.
Specifically, take as many AP/IB courses as you can. It will set you up well for college, and having a lot of gen eds out of the way really helps. Plus, taking a really heavy course load and doing well potentially opens up scholarship opportunities to you.
I took 10 AP classes in high school and came in to college with enough hours to be a sophomore. I'm graduating a semester early. It's nice!