Don't think about anything, just relax your mind. When you come back to do that homework, your mind will be fresh and that hard math problem will suddenly become easier. Join clubs or organizations, even do some volunteer work. You might not want to work your first quarter or semester, until you are sure you can handle the class load and a part-time job. It's better to focus on your schoolwork, without too many distractions.
College is a lot better than high school, but also more difficult.
It is a learning process everyday, whether it's what classes to take or how to study for that first midterm. And, even take some AP classes too if you think you can handle it and the AP test. Otherwise, take the class at a community college so when you attend a CSU or UC school, you can skip over to courses that relate to your major. Some study tips I think would help since your high school study habits won't help in college. When taking notes in class, write down some questions that you might have on one side and the notes on the other.