1. Allow them freedom, but set boundries. Teenagers aren't children, but they aren't adults either. You need to allow them more freedom than adults, but have to set limits.
2. Set an example. Monkey see, monkey do comes to mind. Whether they admit it or not, they see you as an example. If you come late or don't wear nice clothes to class, they'll think that that's ok.
3. Acknowledge their efforts. Everyone wants to be appreciated for a job well done. Some students are better than others, but it doesn't mean that they don't deserve praise.
4. Admit your mistakes. No one's perfect, not even the teacher. If you made a mistake, that's fine, just admit it.
5. Have fun. Being a teenager is tough and school can be stressful. Don't be afraid to have fun in your class. Students don't have to be silent in order to learn. Try using games, music, facebook, twitter, or youtube in class.
6. Motivation is key. Setting goals, using rewards, competition, or their inquisitive nature are all ways to get students motivated.
7. Show some respect. They deserve it. Respect them and you'll see that they'll respect you back.