Know the programs offered. That info is in brochures and on web sites, so no need to ask it in a visit.
That's the best way to prepare. As for questions that aren't easily answered by other sources, I recommend asking a lot of things specific to student life on campus, the strength of the school's career center, etc. Also ask for advice on your situation, if yours is somewhat unusual (this is okay; they'd rather give you advice then have you submit a bad app). This info is harder to come by.
Veritas Prep | GMAT Prep | MBA Admissions Consulting | Co-author, Your MBA Game Plan
Save $100 on Veritas Prep GMAT Courses And Admissions Consulting
For a limited time, receive access to five Veritas Prep Computer Adaptive practice tests when you purchase a Veritas Prep GMAT book! Buy Now!
Enroll now. Pay later. Take advantage of Veritas Prep's flexible payment plan options.
Veritas Prep Reviews