The heritage of values which has been received and handed down is always challenged by the young. --Pope John Paul II
It's a lot easier to find advice about dealing with small children than with teenagers. That's because no one has found what actually works with teenagers. They are big, loud, and strong. Many appear to have made it their mission to disagree with every single thing their parent tells them. And if they cannot intimidate Mom into giving in to their demands, they will try to confuse her into it with stunning feats of illogic. Let's admit it: they can be downright scary.
My advice: On bedrock issues, hold your ground. Sure, a teenager or adolescent needs to be able to decide some things for himself. But stick to your guns on the big stuff. They'll survive the disappointment, and you won't lose respect for yourself. Here's an example. My middle-school son was desperate to attend a co-ed party held at a motel. It included--you guessed it--a sleepover. I told him he could attend to swim and play pool, but at eleven o'clock I'd be there to bring him home. He was outraged and mortified. "But everyone else is sleeping there!" I showed up at eleven and brought him home.
The next day, to his credit, he told me how relieved he was to leave the motel. Up in the bedrooms boys and girls were engaging in activity that made him supremely uncomfortable. He was glad to have an out.
So don't be afraid of the conflict when you say "sorry, but no." Be sure to let them know that you sympathize but need to do your job.