1. Remember it's temporary
    It feels like forever when you're in it. That makes sense: it's your entire teenage/adult life as far as you've ever had one. But it is very temporary, so much so that it will feel like a really funny, vivid blip someday. Remembering it is very temporary should help make the bad times less bad and the good times more good.
  2. Be as social as you can be (without compromising yourself on a fundamental level)
    By far the most important thing you will learn in high school is about how you get along with other people. Never again are you likely to be in such an intimate, all-encompassing situation with such a diverse cross-section of people, who are all as panicked and rapidly changing as you are. Learn who they are and how to get along with them. Push yourself to be social and form connections as much as you can. Be a phony for a while! Just don't compromise who you really are. Deep down you know.
  3. Love your extracurricular activities
    Full on dork-out about something. This will form you more than any class and get you closer to people. Choose something you're passionate about and go all in, or don't do it.
  4. Never don't do your homework
    You can try hard, or not try hard. But never just "don't" do your homework. I mean, what's wrong with you? Bad values, bad result. It's bad if you don't get away with it and probably worse if you do. Always at least DO your homework. Always, always, always.