a current student here
I don't want to write tropes about doing the best you can, being yourself, and all of that jazz. But it's important to realize that once you're in college you have to rely on yourself. You have agency, you make the decisions, and this new found independence can be liberating. At Santa Cruz it's easy to have a social life; but that social life needs to be balanced with studies. The education at this school will end up costing you over $100,000, so you, the prospective student, need to remember that the time spent on this campus is an investment.
This in mind, my main tip is for people who consider themselves anti-social. When you arrive, join an organization or two, and feel uninhibited. There are so many clubs and student organizations that they should be considered part of what you're buying. Joining these clubs will allow you to make more friends than you could ever need, and these friends will expose you to interests that may stay with you for the rest of your natural life. It's so easy to meet new people if you just let them in.