1) Do an official tour. It's a great way to see the campus and get your Fitbit steps in. These tours will provide the most information from your visit from an applicant's standpoint. The admissions folk can answer your queries as an applicant. Remember that these people will likely not show you aspects of the school they dislike, so take it with a grain of salt.
2) Stay overnight with a student. If you have the opportunity, stay with a student in a dorm. This will provide the best insight into student life and your possible living situation. These students are more likely to give an honest perspective. Try to ask them many open ended questions like "What do you wish you knew before applying?" rather than a yes/no question like "Do you like it here?".
3) Sit in on a class. Ask for permission to sit in on a class that you may potentially take as an accepted student. Remember that while the dining options and social life may be great at the school, your primary focus should be on the academic fit.
4) Document your experience. Make sure to take lots of videos and pictures. Write notes to yourself with things you loved or hated. Scribble down questions to come back to. It's important to remember your experience for your application (the dreaded "Why this school?" essay) and eventually for when you are deciding where to attend.
5) Allow yourself to wander. Most of your experience will be highly-structured. Remember to take a look beyond, so you can form your own opinion. With a fully-charged phone armed with Google maps, walk around the quad or pop into the bookstore. If you could forget everything from the school reputation to your parents' preferences- what would you think about the school? Is it for you?