What Not to Do
Don't accuse or argue. If your friend gets angry or provokes you, remind yourself to remain calm and to stay focused on your goal. "I understand that you don't like some things I do, either; we can talk about them later. My point now is that when you drink, you're doing dangerous things."
Don't lecture or moralize. Remain factual, listen, and be nonjudgmental. Remarks like, "You've been acting like a slut," will only elicit defensive anger. Instead say, "You've been hooking up with people you don't like and doing things you regret the next day."
Don't give up! If your friend seems resistant, you can bring it up later or let them know you're there for them if they ever want to talk.