If you are speaking of teenager or perhaps older who lives in your home you lay down the laws of the household and stick to them. That goes for your expectations and their responsibilities as well.
This is a sticky wicket as there is so much more that is harmful to older children now than ever before. Good communication between you is a must and trust does the trick also.
Other people asked questions on similar topics, check out the answers they received:
Other people asked questions on various topics, and are still waiting for answer. Would be great if you can take a sec and answer them