Appropriate age group(s):
Elementary School
Middle School
High School & Beyond

Description of technique:
Recognize and respect the fact that peer pressure is real and that as a parent you will have to deal with it. Constantly fighting with your child about it will be extremely counterproductive. After all, communication is key and if you criticize everything your child and his peers are doing, you'll risk shutting the door on your communication permanently.
It can be very difficult to accept an outrageous hairstyle or a baggy and sloppy wardrobe, but it may be more prudent at times to let these types of expressions slide and to save your strength for the more important life struggles such as stealing, alcohol or drug abuse.
We all need to feel validated. If your child knows that you are willing to accept and respect at least some of their expressions of self as they try to figure out who they are, then chances are they will be more willing to listen to the really important stuff you have to say.