duh....
But seriously. Talk to your recruiter. He/she should be able to point you to a couple of study guides.
On second though... from an email:
Study guide is www.petersons.com/airforce/books.asp Go to right side of page and study book labeled Military Flight Officer’s Aptitude Test. Test you will be taking is Navy and Marine Corps Aviation Selection Test Battery in Section 6 of book.
I only seriously studied for about a week before I took it, and ended up doing alright (7/8/7), but I feel I could have done better.
Print out a copy of the exam and answer key, go through it several times, and concentrate on any area you find difficult. For me, it was the mechanical problems - pulleys etc. I believe there may be another study guide as well but you'll have to wait for someone else to chime in...
Good Luck!