It's incredibly easy, and a lot of fun.
Take the easiest and fewest number of classes you can, ditch them whenever possible.
Don't think you're a loser, don't act like a dick.
Stand up for yourself, get in fights if you have too, but don't go looking for them.
Don't be awkward.
Do whatever you want, your under 18, the worst that will happen is you get suspended.
Don't think you're cool for doing whatever you want.
Stay away from Bros (Wears Tapout, Affliction, or Ed Hardy? Talks about how high they got and how much they love weed? Ignore them, laugh at them)
Be respectful to the teachers, act like an adult and you get treated like an adult.
Fuck your grade point average, just make it good enough to get into a university if that's what you're looking to do. If you're smart enough your SAT or ACT score will pretty much guarantee you getting accepted.
Once you turn 18 and go to college, take your studies more seriously. Find out what your passionate about, and learn as much as you can about it. Don't stress about your classes, don't let them take over your personal life. College is even more fun than high school.