It takes a special person to be able to stand in front of a room of students and teach them something everyday. It takes even more to teach students who are jacked up on hormones, dealing with relationships for the first time, arguing with their parents, and trying to figure out exactly who they are. It is hard enough to get everyone to do an assignment let alone learn anything, still being a high school can be incredibly rewarding.
If you want to be a high school teacher you need to have equal measure of compassion and determination. Teenagers are going through things that they have never had to go through. They are given more freedom, allowed to have cars and jobs, but still have to report to teachers and to their parents. Make sure that you can listen to your students and help them when they are struggling, but know when to push them when they are not working to their potential.
You need to be able to be firm in the classroom. Teenagers can be troublesome and you will have to put your foot down or you will loose control of your classroom. If you do not feel that you could argue with students and parents, then you should probably not become a high school teacher.
You also need to be creative. High school students would usually rather do anything else than be in a school room so you need to make sure that you can make your teaching interesting and engaging. You need to be able to think of new ways to get the students interested in what you are trying to teach.