I wrote a bit of advice to someone asking about how to improve his score, and I realize some other people could probably benefit from this too. It's a rough strategy, and I welcome people to add suggestions to it.
This is geared towards those who are getting less than ~70% of their Verbal correct. As I truly believe just following these simple steps can get you to break that %.
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CR:
1) What is the conclusion?
2) What sentences support the conclusion?
3) What needs to be true for the support to make the conclusion true?
4) Is the question a strengthen, a weaken, or an assumption? (Or a couple others)
SC: (I had a list of all of these but I actually lost it as I became more comfortable, but here are the "main" ones)
1) Check for verb/tense agreement (very common error)
2) If there's a pronoun, immediately check that it has a reference (every time there's a pronoun, this should be next)
3) If there's a clause, what object is the clause referencing?
4) Check for parallel structure for lists and comparisons
5) Apply idiomatic rules (This one is tougher to learn, but there are a few that come up over and over)
RC:
1) Read entire passage
2) Keeping in mind the main point
3) As new information is presented, know why it was presented and how it relates to and develops the main point
4) Answer questions from memory if possible, otherwise refer back to passage.
Again, I think you're at the point where you need to ground yourself on solid fundamentals. I would read some of those guides until you feel comfortable with your approach to questions. When actually doing practice questions, you should never be "guessing" at an answer. Don't worry about time yet (I was spending 5-10 minutes on each question at this point). Give a reason why you think your answer is correct, but also give a reason why each of the other answers are wrong. ONLY AFTER doing that, check to see if you were right. If you turn out to be wrong, understand why your answer was wrong and why their answer was right.