Still a newbie, but having gone through the OG diagnositc now I'd like to point out what might seem obvious in CR questions:

Read the passage very carefully, and be sure to understand every word of the question being asked.

Now this seems obvious, but let's look at one potentially subtle trick that I've seen more than once:

Consider the following CR questions:

"Based on the passage, which of the following must be true?"
"Based on the passage, which of the following could be true?"

"Must be" vs "could be".

A test taker, in haste, might miss the precise wording of the question and either get tripped up and lose time, or worse, select an incorrect answer.

For example, in the "must be true" style of question, there may be multiple answer choices that *could* be true with only one that *must* be true. If you have not correctly read the question, you may quickly get confused and flustered thereby wasting valuable time. Worse yet, if you're the type of test taker who will generally select the first answer you read that satisfies the question being asked, then your incorrect reading of the question itself could lead you to select an incorrect answer.

So just a non-rocket-science suggestion/tip for the CR section of the GMAT!