There are many things that you can write in a paragraph on this topic. In light of this, let me give you a few ideas.
First, like you state, you can start off by saying that teenagers often identify themselves and find their identity is differentiating themselves from others. In this case, they differentiate themselves from their parents by external means.
Second, you might want to talk about how this is said to be a natural process of development and does not have to cause alarm. All people need to discover who they are. Moreover, finding identity can be a hard task.
Third, in light of the second point, parents might want to encourage their children to explore who they are. If parents take this approach, then it might encourage their children. Moreover, they might not see what they are doing as being rebellious. The transition can be much smoother.
that's will help me...