The fact is there is no short cut to solving CR and RC questions. Both work on your comprehension skills.
But there are a lot of areas you can improve on in a short time.
Obviously the first step is to understand where you are facing the most difficulty. Start making error logs and track them. Creating an
error log is just the beginning. You need to document why you missed a question.
It can be
1. Difficulty to comprehend some words - Start taking a note of these words. Understand their meaning. Go back to the questions a few days later and see if it helps.
2. Inability to identify the gist of it - If you can understand each sentence independently.. but not as a whole.. you need to start reading general magazines and articles .. and improve your comprehension skills
3. Finding the answer to be obvious after seeing the explanation - Mostly because you skim or point 4.
4. Bringing in outside information or making your own assumptions - This is the most annoying and most diff.. writing the key points and assumptions down will help. But you obviously need to work out some short hand way to do it.
5. Problem in understanding what the question stem needs - The presentation will help
6. Taking a long time in solving it ( Timing is the only issue) - Practise..
Just curious , are you doing better with GMATPREP and
OG questions and not with other question banks. If that is so , I would not fret too much about it. Just good practice is sufficient.
Some of the CR questions from other vendors are ridiculous and ambiguous. Chances of seeing such a question in GMAT is relatively low.
And on a side note.. All these diagramming can only help if you start forcefully applying the method for every problem you see. It might need a lot of practice. If you don't have the time..suggest reducing the time spent on diagramming and notes
Cheers
Mazerath