1st call now to see their policy on school visits. Some schools do not offer this and would rather have students attend the Open House.
When you call they will tell you what is a good day to come since exam, meetings, holidays etc. come into play. Also they may want you to see the students when they have OMM/anatomy/lecture. Or you can tell them what you are hoping to see and hopefully will work it out.
figure out if they have housing for you if you need it. Try to tailor it to what you want to see (lecuture, PBL session, OMM, anatomy, etc.) but be flexible.
Remind the Dean or whoever is setting this up 1 week before your scheduled date. try to at least say hi to the dean. Introduce yourself.
try to get assigned to a 1st year/ 2nd year to ask questions 1-on-1