I second all that's been said so far. Talking and listening is at the top of my list. And that really needs to begin way before they are teenagers.
I also feel that being a parent and not a friend is important too. You can become friends when they are grown. They really want you to be an authority figure whether they act like it or not.
Also, don't threaten and not follow through. When I tell my kids that these are the consequences for certain behavior, they know that I really mean what I say.
I have found that getting along with my 15 year old son is a lot easier than with my 13 year old daughter. I have to be much more patient and just step back sometimes and let her yell.
We talk a lot. I've told them both that the one thing they don't want to do is abuse our trust in them. It's very hard to earn it back.
I've also said that the older they get, the more freedom that they get. This also ties into the trust issue.
And remember, they won't tell you everything but if you get on a good footing of talking, you'll hear most everything sooner or later, even if its months on down the road.
And don't blow up if you hear something that you don't like. Stay calm, maybe asking if you can discuss this in a little while after you have time to calm down and think.
Give them an opportunity to make decisions, but maybe letting them know how you really feel. Just yesterday my son and I had a discussion about him meeting a girl from another town over an hour away at Starbucks. She was driving here and I had some issues. While I didn't mind him meeting her, I didn't really care for it and told him so. I didn't think it was wise for her to be driving through very heavy, rush hour traffic just to meet him (they've never met before, she's a friend of a friend of his). Plus, she was supposed to be coming to our town to watch some of her classmates play against a local private school not visiting him. I asked if her parents really knew why she was coming. So, I left it up to him whether or not he met her. He decided not to meet her.
I hope that you get some of the answers you were looking for.