Familiarize yourself with the test format, know what kinds of questions will appear in what sections....maybe take a self timed practice from the ARCO book.

You cant know what exactly to study so I settled for knowing what kinds of questions and the sections of the test.

I took my AFOQT in December 07, and I used the ARCO 6th edition. It worked great, but I dont know what to tell ya about the 4th edition....