Could you please give more details concerning your preparation and also what problems exactly do you face when trying to solve RC questions? Are you able to understand RC passages and answer choices fully or do you sometimes struggle with difficult vocabulary?

Reading comprehension,is something where you can definitely find and fine tune a strategy. Did you try the various strategies to tackle RC, or did you just read one and went along with it? As Katia said, it would be best to analyse what is going wrong in RC, do have a problem with vocabulary and harder more intense passages etc. Are you just reading just for the sake of reading or are you "strategically reading"...You should try a few approaches to RC, and see which strategy works best for you. Once you have the strategy locked down, its just a matter of being comfortable with it, and unlike SC where you would be well served with attempting hundreds of practice questions, in RC you can get away with far less practice provided you master your strategy and familiarize yourself with reading heavy passages.

One more Point - In my case (i took the GMAT around a month back) RC accuracy was direcly dependent on how quickly and efficiently i went through SC and CR, the more time i had, the better i could "comprehend" the passage and then answer the questions. My accuracy went down considerably when i had less and less time. Therefore, your accuracy may depend upon how long you take on average per SC and CR question.

Hi The same case exist with me. Can you please guide me the best book(Other than official guide) to start the preparation again.
What About the Kaplan Verbal Workbook?