If I could add on to the already great suggestions:
Definitely use the many available on-line resources to study for the knowledge-based exam.
Take time to prepare for the exam. (I recommend allowing 1 week per topic area)
Don't assume that because you have been in the industry a long time that you will recall everything you've experienced or learned. Even if you think you will, the time spent reviewing and taking the practice tests is well worth it.
Start early on your work product submission.
For the Designing Learning work product, I recommend a minimum 40 hours to compile the materials for submission. That's above and beyond the time it takes to actually design the learning.
It definitely takes work, but it also incredibly rewarding when it’s achieved.

Terry Olivi, CPLP
2007 CCASTD Co-VP of Marketing