1. Do your homework!
A number of resources exist (both online & off) to guide you in your boarding school search. Check out school sites, brochures, boarding school directories (like AdmissionsQuest of course), etc. to get to know the schools that interest you. This will give you a feel for the schools before you arrive on their campuses.
2. Don't be afraid to ask questions
As you do your boarding school homework, you'll likely come up with a number of questions that cover a broad range of areas - academics to life outside of the classroom. Don't be afraid to ask your guide or interviewer while on campus. It's your chance to learn firsthand from members of each school's community.
3. Pay careful attention to the dorms & residential life program
While on tour pay careful attention to the dorms. Find out where students in your incoming class tend to live and ask to see those dorms/rooms. Ask about study hours in the dorms. How are most evenings structured? What time is the study hall?
Don't forget about the weekends. Are there regular trips off-campus to the mall, movies, nearby towns & cities, etc? What kind of events happen on-campus?
4. Arrange to attend a class (or two or three...)
This is a great way to get a feel for a school's academics. Be sure to arrange a class visit in advance since not all schools make them a standard part of a tour. After class see if you can spend a minute or two talking with students & the teacher. Time may be tight, but this is another chance to learn from community members.
5. Visit the library
Go and take a look at each school's library. Browse the collections, check out the available technology, seek out the study spaces, chat with the librarians, etc. Wherever you go to school, you'll likely spend a lot of time in the library so don't miss this opportunity to explore while on the campuses.
6. See where extracurriculars (athletics, arts, etc) take place
Make sure to visit each school's gym, arts center, theater, etc. If time is tight make it a priority to visit the buildings where the activities of most interest to you take place.
7. Don't forget to try the food!
Goes without saying, but... grab a bite to eat in the cafeteria. Don't pass up a chance to see what a meal is like. The cafeteria will become a fast friend wherever you end up going so get to know it now.
8. Write down your impressions soon after finishing your tours
Always a good idea to jot down your like/dislikes as soon as you leave each campus. It's important to write these things down while they're still fresh in your mind. These notes will come in handy when the time comes to chose between acceptances.