Taking a trip to the schools under consideration can be a valuable experience in your application process. Flexible in their aims, these visits can be completed to good effect either before, during, or after the application season. Whether your intent is to learn more about the "feel" of the school, speak with current students, or discuss your qualifications with program administrators, a school visit aids your admissions process immeasurably. 

One of these immeasurable gains is in learning more about the school. By doing so, of course, you will be helping to improve the focus and specificity of your application, but more importantly you will get a sense on how you might fit in with this program and this campus. Sitting in the library stacks, watching interactions across the quadrangle, reading the school newspaper, and overhearing student conversations are all nonobtrusive means to gauging the ephemeral "quality of social life." Less timid graduate school hopefuls might also attempt something known as "actually talking with someone" for the same effect. In any event, you should leave the school with a much better sense of the school's intellectual and social climate. 

If you decide to interview (these are generally optional), follow all those standard rules about eye contact, conservative dress, self-confident presentation, and so forth. Know the specifics about the program in which you are interested, read the school paper for up-to-date news, and be prepared with intelligent questions to ask. Interviews which are not mandatory for the admissions process are generally quite less rigorous than ordinary, and often turn into a sort of mutual question-and-answer session. Regardless of this informality, your interpersonal skills, maturity, professionalism, and ability to communicate effectively should permeate the interview. If you are terrible at interviewing, don't be afraid to shy away from such meetings (sickness and travel costs are two perennial excuses that work), or to practice your skills with some lower ranked schools before approaching your top choices. If you are great in person, greet the opportunity to interview with open arms and a ready smile. It's usually not a deciding factor, but every little bit counts.