allen: I have found that for CR and RC, experience from doing many, many questions is the most valuable tool you can bring into the test center. Once you have seen hundreds of examples of these question types you should be able to anticipate the answers to questions sometimes even before you read the answer choices. When I prepped for the LSAT I had exposure to countless difficult CR and RC questions, so I was lucky to have a good base there.
It's different for SC. SC is an easier section to prepare for because there is a finite number of things that they can spring on you and they are all basically covered in the
MGMAT SC Guide (and other books too I'm sure). You need to be comfortable recognizing the major patterns (verb tense, pronoun/modifier, concision) and you should avoid as much as possible "going with your gut." For that reason, I recommend reviewing both the questions you get right and the ones you get wrong in SC, reading the explanations carefully. You want to get to a point where you can answer a SC and specifically point to the reasons why the other 4 answer choices are incorrect. Doing SC questions by "feel" (reading all of the choices and picking the one that sounds best), works sometimes, but it won't be consistent enough to guarantee you the score you want.
Make a list of idioms that you've learned while doing problems. Do SC questions in batches of 10 and immediately review the answers. Keep a good
error log and redo questions you got incorrect (or did too slowly) periodically.
Hope that helps!