There is one simple approach that I always take when tackling these sorts of questions.
RC- I read the passage to understand it. (although Kaplan may not agree with this method) That way, when I read the corresponding questions I already have an idea of what the answer should be before I even look at the answer choices.
CR- Before reading the passage, I read the accompanying question.
After reading the passage, I poke holes in the argument and tackle it as if it were someone talking to me (I love to argue). In real life when someone is arguing with you, you always look for the weakness in their argument, right? Well, that's what I do with CR passages. The answer is usually what I thought it was before even reading the answer choices.
Also, be wary of questions like this: 'Which of the following does NOT support the above argument.'
Although you may be compelled to look for the answer that weakens the argument, make sure you look for the answer that doesn't weaken the argument and doesn't support it either. That is usually the correct one.
I hope this helps.