I say, try to be friends with everyone you can. You can learn a lot from the different social cliques that exist in a high school. Stand up for people who can't stand up for themselves, it will make you feel good, gives you a sense of importance and people will respect you for it. Make nice with your teachers so later in HS you can get a cushy "TA" period where you have to do really awful things like "get me a red bull from the store." Stay active in music, play with older guys; I mean you are a bass player and bass players are in demand, plus people love bands especially hot girls. Go out for a sport, football, baseball, tennis, cross country, it doesn't matter, it will keep you in shape and girls like hot guys with muscles. Don't talk S@#$ about people you don't like, it makes you look weak and crass, and nobody likes crass people. Don't try to be cooler than you are, that is if you are a metal kid, be a metal kid, don't buy a ton of clothes from abercrombie to fit in, people will like you for who you are. Do the work, no one likes to look like a smacked a$$ in front of their classmates, plus hot chicks like smart guys that can help them with their homework. Don't be a "wallflower," get out there and meet new people, you never know who you can meet (just like TB). Even if you get rejected by people, who cares? You do not need their approval. I am not going to tell you not to drink or do drugs, but these things certainly do not make you cool, but everyone tries it at some point. Just be yourself... and be as awesome as possible!
I read some other posts and I never got beat up by older kids, and the only time I got into fights was when kids would pick on kids that were incapable of standing up for themselves. Also, some AP classes are BS. I was supposed to be almost done with my freshman year because of AP classes and I had to re-take the majority of them in college. However, they do prepare you for the workload so if you are comfortable taking them, go right ahead. When things look down, just ask yourself, "how can I be awesome?" When you find your answer, things will turn around fast.