because all the "good" answers have already been given, i can only tell you what NOT to do
stay away from the cissp in 21 days book, way to high level and does not cover the thing that is mostly required (CISSP "mindset" which can only be obtained from the original material).
also the CISSP for dummies was mostly a waste of time. some areas were covered perfectly, while others were lacking and some even too deep (way to technical for the exam).
on the other hand, a few good tips that came from CFD are:
get some earplugs. i really hated to be in a room with 100 people all eating, drinken and moaning about the difficutly of the exam.
get plenty to eat/drink for yourself, 6 hours is killing!
schedule some breaks, it will improve your focus and speed during the exam.
don't plan anything after the exam, maybe the only thing you want to do is grab a beer (with some friends if you prefer).
good luck and tell us how you did!