Make sure you are aware of all the deadlines, for all pieces of the applications. There may be separate deadlines or processes for admission and for research/teaching assistantships or things like that. And make sure you know what various pieces are required for each school (i.e., does anyone require a specific subject GRE in addition to the general test? Are letters of recommendation required and how many?) Don't disqualify yourself right out of the gate. With as many applications as some schools receive, the easy first cuts are the ones that don't follow simple directions.

I agree with Isaac about cramming for the exam itself. The main thing your books and practice tests/courses are doing for you is teaching you how the test works and what to expect/how to handle the various sections of it, which is important to maximize your score. And it's giving you a psychological boost of feeling prepared.

Good luck!