Continue to get good grades. Don't slack off even if its your senior year. Colleges still look at your final transcripts. Once you have committed to the college. Make sure you read all emails they send you. Connect with them via social media as well. They will start to send you room/dorm selection. Sometimes this is on a first come basis and you want to get into a good building. Also attend their summer orientation, good way to meet fellow students and possible roommate. Depending on far the school is, pack essentials (clothes for summer/fall/some winter). There is always a Target or Walmart near by to get any larger items. Get involved, join clubs. Have fun, but not too much. Show up on time to class and prepared. Good Luck!
I will reiterate the points that Veronica made in the point above - maintain your academic status, read the emails they send to you, definitely go to their orientation programs (depending on the school, you might be picking your classes during it), and make sure to pack at least the essentials. Senior year is an exciting time with a lot to experience. But it is important to continue doing the things that go you to where you are today. If you have the means to, visiting the schools you are applying to and ask current students what it is like to go to that school. If you are able to, sitting in on a class in a major you are interested in can be insightful. And talk to your friends or peers who recently went to school about how their transition between high school and college went. College is an exciting transition. Good luck!