First thing: Get some good prep materials right away. My personal recommendations:
1) Official Guide (easist to get at
https://www.mba.com) - a must for practice questions, about 1400 of them
2) Powerprep tests, the official ones (old ones), free download from mba.com
3) Cracking the GMAT 2005 book with CD from Princeton Review. The best strategies, period. This book is a must for understanding the test, and it has 4 practice tests on CD plus access to another one online.
Once you have your practice materials, set a steady schedule for yourself. I would first read through PR's book to get a good feel for the test and how it's designed (and how to beat the pitfalls built into it). Then plan on 2-3 hours of practice questions on weeknights, and one full practice test each weekend. Fully review your results and maintain an
error log (there is some great info about that on this site) so that you can best track your progress.
And of course, come join us here in the forums as often as you need to for help as you go along!