A good guide to the whole process, as well as information on what graduate school is like, is Getting What You Came For: The Smart Student's Guide to Earning a Master's or a Ph.D. by Robert L. Peters (Noonday Press, New York). Swem Library has one or two copies that should be on permanent overnight reserve, the advising office has another copy, and the campus bookstore tries to keep copies in stock for sale.
The W&M Career Center has also posted useful information about planning for graduate school.
Most graduate programs offer detailed information through their websites, including: faculty and their research interests, contact people, and admission and graduation requirements. Reviewing the descriptions of faculty research and publications is often the best way to start checking out potential graduate mentors.
The quality of a graduate program will affect both the academic experience and future job prospects--but it isn’t so easy to rank graduate programs by quality. A good first indicator is the general academic reputation of a school (although good schools can have bad programs, and weak schools can have excellent programs in a few areas). Research Doctorate Programs in the United States offers a ranking of graduate programs and is quite accurate. Its weakness is that many subdisciplines are not ranked separately. Swem Library has a copy in the Reference Section (Q180.N334 1995).
The best strategy for deciding where to apply is to rank the programs offering the right areas of study and then submit 3-10 applications, including several programs that seem likely to grant admission. Also applying to 2-3 much better programs and to 2-3 weaker programs should result in a very good chance of getting in somewhere, and possibly the option to go to a top program.
Note that the W&M Career Center is building an alumni database containing self-provided GPAs, GRE scores, schools applied to, and schools offering admission to previous William and Mary students. There should be data for the classes of 94 onward (about half of the members of each class respond to the surveys). This is a great way to get some sense of how students with varying credentials have succeeded in the years after graduation.
Generally it’s best to attend the best or one of the best Ph.D. programs that grants admission. Our experience is that W&M students rarely fail to complete a top-notch Ph.D. program because they lacked the intellectual tools. Instead, they found that they just don't love the field enough to work so hard, had trouble with the expectations or pressures in the department, or were just not happy with their living environment. When those students switched to another program, they, too, achieved success.
For master's students, entering a top program is a mixed blessing. Master's students at an excellent Ph.D. program can be ignored by many or most professors, can get last choice for any teaching or research assistantships, and must compete with the Ph.D. students in classes. These downsides can be balanced by great training, a degree that carries the impressive name of that school, and the possibility of excellent letters of recommendation from people who are at the top of their academic field.