If your child is showing undesirable behavior, she needs your guidance and support so she can solve her own problems. She doesn't need your direct orders. Sixth-graders want to be treated with respect and make choices that satisfy both them and their parents. Sometimes your child will use your rules to help him say no to his friends. He may argue about these rules, but rules do help a child say no.
Rules provide structure.
Fair rules are very important at this age. Consider negotiating and compromising on some rules, like curfew, clothing and hair styles. Save your energy and your child's attention for the important issues. Parents often are so concerned about negative or troublesome peer pressure that they forget friends can be a positive force in a child's life. For example, if your child's peers stress achievement and good grades, your child will probably strive to earn good grades.