a. Make a clear statement acknowledging that a rule was broken
b. State that this type of behavior is not acceptable
c. Declare the rule still stands.
"You came home past your curfew yesterday. This is not acceptable. I want you home by 10pm and on time moving forward." Although they may respond about how it isn't fair or that all of their friends have later curfews, and that you can't make them follow the rule, you can respond with: "That's correct, I can't make you, but that is when I want you home by." Again, although they may respond with an eye roll, grumble or statement of "I don't care," they do care and the rule will have some impact on their decision making in the future. And since teenagers still care about parental approval, continue to give them specific positive praise, acknowledging when they do do something you like.
Reference: Nichols, M. P. 2009. Inside Family Therapy: A case study in family healing. Allyn and Bacon. Boston, MA.