Hold true to yourself and your beliefs. I live in a skanky redneck town that is full of drinking and drugs, but I have never done anything not even smoked 1 cigarette. I have always been very against drugs and I'm proud to say I never fell to pear-pressure. I stayed away from parties that I knew were going to have drinking and drugs. Yes there were times I was offered drugs, it's not always possible to stay away from them, but you don't have to take them- I never did. I was always the "go to girl" my friends all knew if they were at a party and needed an out they could call anytime day or night and I'd be there for them.
Also try to keep a good relationship with your parents. I didn't (and still don't) have a good relationship with my mom. She was never there for me. My dad on the other hand was always there for me. He helped me with homework when I needed it. I could call him whenever and wherever and he'd pick me up if I needed him to. He was always there for my friends too, he went out late one night to change my friends flat tire when she needed help.