Do not criticize: Teens are a very sensitive and critical bunch so think carefully before you say something that can be considered as being critical of their appearance, friends or activities. At this phase teens tend to display more loyalty and allegiance to their friends than their own family. This is understandable as their peers are privy to their secrets and encourage them in literally following their heart unlike parents.
Discuss your adolescence: Fact is despite the generation gap, hormones and their effects remain much the same on all parts of the globe and over the centuries. Discuss how your teenage years were and how you felt growing up in a different era with more restrictions and fewer opportunities to socialize. Talk about the advantages and disadvantages of your teens versus theirs. This way your children will see you as someone who has also navigated the same choppy waters and can be consulted and confided in when the need arises. If you feel they are having sex, you absolutely need to discuss it no matter how uncomfortable it is. Doing this might save a lot of trouble later on.