If you know the college you're attending, go hang out, even if it's just sitting outside. You'll get a little bit comfortable. Okay, sounds geeky maybe, but you can call the school or the health people and ask them to ease you in.
What I would do if I were you is to review your SAT scores and especially understand how you did in various types of questions. I would them inquire as to the minimum requirements for entry into the college you are going to attend as well as the average of the student body. I would evaluate where you are compared to where the student body will be,
If you find that you are below the student minimum requirements in an area I would not panic but I would seek out remedial texts in that area or try to do some learning online. .
Well, that depends on what aspect you want to be prepared for. A decent everything guide is The Naked Roommate, but college will always be a big change that a book can't fully prepare you for. Academically, look at AP or IB level textbooks (your school system may have them listed online, or you can ask a teacher), learn a good study method and learn to take good notes. Also, learn good highlighting technique if you don't already know a good method. Socially, remember to keep your door open for a the first week (when you're in your room and awake) so people will talk to you, and don't be shy about approaching people on your hall or in classes who express opinions or points that interest you.