Go. Although most colleges say they require orientation, in all likelihood you can skip orientation and still attend school in the fall. But that's a mistake. You'll feel much more self-assured if you spend some time on campus before school actually starts. And you'll be able to get all your questions answered.
Set your schedule for the fall term. This can be confusing if you've never done it before, but advisers from your major will be available to help you choose classes. Doing this now helps avoid long lines at the beginning of the semester.
Meet as many professors as you can in your particular major. Try to stand out, but don't act silly. Ask mature and engaging questions.
Make friends. This isn't the time to be shy and standoffish. Participate in everything. And remember, everyone there is as nervous as you are.
Learn your way around campus. A big university can be overwhelming when you're trying to find your classes. Don't sit in the dorm room during down time. Get together with some other kids, and walk around.
Get information on extracurricular activities. Colleges and universities have an unbelievable number of clubs, organizations and other activities. There's at least one for everybody, and there will likely be representatives from these groups at orientation. You will also learn about the sororities and fraternities at your school.
Encourage your parents to attend freshman orientation. It's not embarrassing to have them with you, because all the other students' parents will be there, too. Many colleges have special dinners and meetings for parents during orientation.