Ok, first off I want to thank everyone on these forums for being more help to wannabe's like me than anyone or any book could ever be. I took the ASTB about a month ago and pulled off an 8/9/8 61, so I want to try to pass on the help I was given.
First of all, buy the study guides. I bought the ARCO Military Flight, ARCO Officer Candidate, and Barron's Military Flight test books. The information in these books is very valuable. They may not cover exactly what is on the exam, but you can't expect that. What they do is give you an idea of what kind of questions to expect. The practice tests are the best way for you to put yourself in the scenario of what the actual test will be like, and one of the only ways to see if you're working at too slow of a pace.
Second, use the Marine gouge website and all of the files that they have available. The information on this website is very very similar to what the test questions are. The questions may not be the same, but most of the concepts are. If something seems vague to you while studying, look it up online. Try to think 'how else could they ask this question?'. There is a lot of information to know, and 90% of it won't be on your test, so don't focus too much on one thing if it is bothering you.
Third, if you have any questions feel free to PM me and (without giving you exact test material) I will try to help. I have attached my personally compiled study guide. It consists of information gathered from all 3 study guides, this forum, and many miscellaneous things that I thought might help. Keep in mind that I am not going to tell you what stuff is 'more important' than other things. I used this to keep myself organized, so it might be useful for some of you to add or remove things as you please. Also, I'm human so some of the information in this document may not even be correct. I tried to make sure it was, but I may have made a few mistakes without noticing them.
If you use this to study, let me know after you take the test if it was helpful at all. Good luck to everyone that is yet to take it, try not to stress too much.
Patrick