What should you know? Know a little something about all of the faculty. Not life histories, but basics like their research area. If you know who you will be interviewed by, make sure that you're familiar with their work. You're likely to be asked how your interests match up with theirs, so it's important to know a something about their work. You don't have to know it all. In fact, prepare some thoughtful questions that shows that you've done your homework and lets you know a bit more about the faculty member's work so that you can best explain how your interests fit with theirs.
What else should you know? The program's orientation. For example, is it oriented towards theory or application? General requirements. Again, prepare thoughtful questions to ask faculty and students.
