I think I need more information to help you. I'd love to give you suggestions, but I don't know what you are already doing, the age of your high school students, what they are doing that causes the chaos, etc.
How engaging are your lessons? Generally speaking, the more engaging your lesson, the less likely you will have behavioral problems. This isn't always true, but as they told us in my teacher prep. program: "The best classroom management strategy we can teach you is good lesson planning!" It's so true!
Good luck! Know that this is something even veteran's teachers struggle with. It doesn't mean you are a bad teacher. It will get better! Please post more information, as I would love to help!
