What everyone said above is true so I won't repeat it. I would like to add 2 things, 1) When faced with a comprehensive theory exam, I purchased the top 5 levels of 2 well known methods and completed them which seriously reinforced all of the basic facts. 2) FLASHCARDS!!
Music theory may make up a comprehensive whole, but to get there, there are lots and lots of little individual bits. The absolute fastest way to get all of the facts completely nailed down is flashcards (they also work great in college science classes!). Making your own by the dozen will also help you a lot. Be sure to put the answer on the back so that you can check your answers. In lots of circumstances, especially on exams, it's not the big things that get you, it's the little ones.