Think of the tour like a shopping trip. You want to be able to get the most information you can while you are there, but also to inspect the campus. So, most likely the first stop is the admission office. Since this is a rather important place, the first stop for most families, how have they designed it? Does it feel warm and welcoming? What kinds of materials do they have out to read?
As you go on the tour, have a parent take pictures you can catalog later to remind you of the buildings and what you saw. Schools tend to melt together if you are visiting lots of schools on a trip. Plus this will help you later. Read the message boards and see what things are happening on campus. See what students think is important, check out study abroad opportunities, internships, concerts etc...
Definitely check out the dorms, but make sure they are taking you to the Freshman dorms. What are the living arrangements. Also remember that most dorm rooms are smaller than you room at home. But think about living there.
Be sure to ask your guide good, solid questions. Ask them where else they applied, why did they choose this school over others they were accepted to. What do they like? What would they change?
As you walk around check out what kids are wearing, listen in to their conversations? What are they talking about? Is the content about the class they just took or research project or are the complaining about something?
In the information session, make sure you ask any lingering questions you may have about applying, opportunities, etc... If you are from another state or country, see if you can get an email address of student from your home so you can contact them. Definitely ask for a business card from someone in admissions who represents your region, state or country.
Finally, keep a record of each school and your thoughts about the campus and things you liked and disliked. This will be important later. Can you imagine yourself there? Why?
Have fun with the visit. But keep an open mind. You never know what you will find.