First off, without knowing the person or sitting down face to face it is hard to give "good" advice about grad school in general (sorry).

For example: What are your expectaions for grad school? What are your long term goals? What is your modivation for even considering grad school?

This kind of falls along the lines of just general advice on considering grad school. For more of this type of general advice you can get more information and advice in other articles posted here as well as looking at other sites such as www.phds.org.

For general info on schools and such, you can do your homework by looking at listings and rankings of schools such as the us news's graduate school rankings and/or others. You might also look at The Chronicle of Higher Education.

Some general advice about "non-standard" areas such as combinatorics: check out the department and make sure there are "several" people in that area and also look for things like a regular combinatorics seminar.

This advice is all pretty "obvious" but if you haven't thought of some of these things already hopefully you may find this useful.