Need help with the ASVAB?

Okay so I'm trying to join the Marines, and yesterday I went into the recruiting office and took the practice ASVAB which consists of the four hardest parts of the test. (Math, vocabulary, paragraph comprehension, and arithmetic). I scored a 28...I am so pissed. Everyone was telling me how easy this damn test was, and I just failed it so quickly, I feel like an idiot. So anyways, my recruiter let me borrow the "ASVAB for Dummies" book. But I don't really know how I should study it. This is a different type of test. It's like stuff you either know or you don't. I just need to know how I should study this damn thing, because I have been wanting to join the Military for many years, and my life time dream would be crushed of I couldn't get in.