Know what you want and especially what you don't want. Stick to that, on every level. Don't be persuaded. Don't stay longer if you don't feel the need to. Don't get in the car with someone who is under the influence. Don't kiss or have sex with someone if you don't feel like it. If it doesn't feel good to use drugs when your friends do, then don't do it. And the same applies the other way around. Just as you have boundaries, so does someone else. So don't try to convince someone to do something against their will. Respect your own boundaries and those of others.