you are probably going to find a lot of variation with this, but i think most would agree that the basics are:
are your numbers a practical fit with theirs? (ie are your numbers somewhat around the mean with either their average gpa or mcat or both)
location (it is four years of your life, so you better like, or at least be able to cope with where the school is located)
this is a great resource, so if you have questions on specific schools, definitely post. best of luck
tuition (this is really a huge one if you have the option of going to your state school, i have heard of a lot of people that have turned down more prestigious schools because they got into their state school, the difference in price is enormous, like 20k a year or so)from the info you can dig up on the school does it seem like you would excel there
research (there are definitely schools that are more research oriented, so if your into that thing and don't want a phd, then dig up info on how available research projects are)
prestige (i really think this one is over rated, but a lot of people put a lot of merit into top 25 schools)