I recommend taking a look at the academic side. You want to know if the university will provide you with a great education in your field of choice. If you’re completely starting from scratch but have a vague idea of what you’d be interested in, Google “Best universities for [insert field of interest]”. US News is a reliable resource to click on for a list. You do not have to apply to the top universities in the field if you don’t want to but you now have a list of 100+ to choose from. If you genuinely have NO idea of what you’d like to explore, then simply use the College Search Tool mentioned in the previous response to create a list.
If you’re a science student, take a look at the research opportunities available to a student. Afterwards, search for the Student Organizations available on campus. Do you see anything you’d be interested in? Depending on the size of the university, options may range from 60 -200+, so it’s important to figure out how you can explore your interests and hobbies once you’re there.
Finally, what else are you interested in? Study Abroad? Sports? Take some time and just explore the university’s website. By simple shuffling around the website, you’ll learn about what the university values and the general atmosphere the university is trying to create.