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By aviation test, I'm assuming ASTB?
If so, download the practice test from this site (
http://www.airwarriors.com/forum/showthread.php?t=5804 , go to the second post). I used this as well as searching for information on google about a few of the topics on the test that were not answered well. Also, if you or a friend has some old math and physics books, they help in refreshing your memory on the math and mechanical portions.
The spacial section is not included in this prep test, but if you have a flight simulator, it will help. Just turn down the realism as far as stalling and such (just one less thing to worry about) and look at the horizon as you turn, dive, climb. Do some of these and look at 3rd person view to see what your plane looks like.
Anyway, doing this helped me out a great deal. I just took the test this morning and maxed each section. You may also want to look under the "Commisioning Programs > ASTB" link on the main forum page for more information.