Take leadership opportunities, go to all of your athletic events with friends, hang out with a bunch of people, find out who you want to stay friends with after school (you may be surprised how many you end up keeping in touch with, I was), and party so you're prepared for college.  Blackout with your buddies before it happens in college and you wake up in a slight state of panic thinking "what the fuck just happened?"
The main problem with my high school was that there were a lot of really snobby, bitchy, pussies.  A lot of girls were extremely anti-party until the day we graduated because the school was so fucking up-tight about it, so partying was tough sometimes.  You're going to love college a lot more (if you have basic social skills and a work ethic).