Location, Age, Garage, Basement, Lot Size are some of the other big ones. 

One thing I try and do is think about the target buyer of the subject home. What other homes would that target buyer be interested in, those are your comps. The answer can vary from house to house, as the answer can be commuting location, school district, in law suite, garage size, basically anything that would make the target buyer want that particular home. 

Hope this helps! Aaron