That said, the best practice you can hope for is to INTERVIEW AT A LOT OF OTHER PLACES FIRST. Just trust me on this. Interviews require practice, and the best way to do it is to interview at other places that are good. If you don't trust me, listen to this guy, who says the same thing (and got the job at Google) [http://paultyma.blogspot.com/2010/11/google-interviewing-sto...].
That all said, you will probably want to review your basics of analysis (e.g., big O), as well as things like binary search. You will probably get asked to implement code of some sort, so be really well acquainted with your favorite language. Pick up a copy of Programming Pearls, by Jon Bentley, and work through a problem or two every day. By "work through", I mean try and do it yourself, and THEN look at the answers. The idea is to be thinking well come time for the interview.
Other things everyone knows are, you want to be really well acquainted with what Google is doing in your area. One of the ways they vet candidates is to see who actually knows what Google is an does in practice, rather than asking why they want to work there. A lot of their questions will probably come from problems they actually have.
Brush up on your books from college. Give the algorithms and data structures 101 stuff a quick look over and make sure you understand it.
That's not a comprehensive list or anything, but if you want more material or advice, and you don't want to divulge more information here for whatever reason, feel free to hit me up.