If you are considering graduate study in philosophy, you need to know how to prepare for it. Because there are different styles of philosophy, your optimal undergraduate program may well be affected by what sort of philosophy you aim to pursue in your graduate work.
The most important way to begin preparing is to talk to members of the faculty about the kind of work you are interested in doing and get their advice about which graduate programs you should be considering and what kind of preparation they require. Faculty members are by far the best sources of this sort of information. Too many students fail to seek advice until it's too late to devise an optimal course of study. Even if you are not sure that you might want to do graduate work, it's important to seek advice early. Each fall the Department has a meeting to discuss issues about graduate education with students who are considering making an application.
The guide books you find in book stores will probably not be very helpful to you. Things change too quickly for them to remain in date. But you should consult the internet resources linked to the UM Tanner Library web site, including the Philosophical Gourmet Report. Additionally you could look at the APA Grad Guide as a source of information.