I have a couple of "drills" I've been doing to work on verbal, to practice comprehension while reading the passages for RC and the arguments for CR. You may or may not find them useful.
Before I detail them, I'd just like to say from the get-go that: a) this is not a ground-breaking innovative approach and b) i'm not a GMAT expert, just a fellow test taker.
Anyways, for critical reasoning, take a set of problems. These can be problems you've already done!
For each problem, forget the actual question stem. Just focus on the argument.
Read through the problem, identifying what each sentence (and each clause) are doing. IE what is the purpose.
For each sentence, write out (a) the purpose, and (b) the sentence in your own phrasing.
After you've finished this, find the structure of the argument.
Try to accomplish this within 45 or 60 seconds. Once this is mapped out, it should only take you 15 or 30 seconds max to identify the correct answer choice if you have a good understanding of the argument.
I think you'll find that once you've become comfortable picking out how the argument is formed, it'll be significantly easier for you to point out the weaknesses (ie answer the questions)
For reading comprehension, you're basically going to want to do the same thing. Forget the questions, just practice getting a good understanding of the passage. With a good understanding of the passage, picking the right answer choice becomes much easier.