If you're looking into AP classes, you are probably already taking the toughest classes that your school offers. That's a good start.

What can you do on top of this? Well, if you're interested, I'm sure local colleges offer advanced classes in practically anything you'd like. Try looking into some college-level curricula on top of the current courses you're taking in HS.

Another option is self-study. I knew tons of students who studied AP courses on their own time and took AP tests afterwards. If you plan to do this, then I would try to speak to a teacher or a guidance counselor to set up a formalized advisor for the AP self-study course you're interested in to keep you on track as you study.

Take added classes at a local university or try self-study. I did self-study for AP Micro-Econ back in HS and got a 4--so it's not impossible to teach yourself. Plus, I think this will be a great talking point in your college interviews: "I thought I wasn't getting enough, so I took it in my own hands to study advanced topics not offered by my school."

In addition to doing well on the SAT and ACT, try to join more activities. Sports, music,clubs etc. This shows colleges that you're a serious student, but you have many other hobbies. Colleges want wholesome people (people who like many different things)...

Be active in your community and get some community service hours. This can range from just working at your local library or even helping a teacher out in need of services.

Also try to join as many clubs as you possibly can because this is what colleges are looking for. Someone who is smart, active in their community, and communative.