A key to understanding your teenager is knowing who her or his friends are. Make a point of getting to know the parents of your child's friends. Allow your son or daughter to bring their friends home. In fact, encourage the use of your house as a meeting place. Lead by example, or to put it another way, walk the talk.
Teenagers are very sensitive to hypocrisy in adults.
Make sure that your actions are consistent with your values. For example, if you preach honesty and then cheat on your income taxes, you send a mixed message to your child. If you want to raise your teenager to become an honest adult, be one yourself. Pick and choose your battles. Your kids need room to experiment with who they are just as you did when you were a teenager.