Hi Aman,
Assuming that you mean the Verbal Reasoning section of the GRE, you need to first master vocabulary in order to score higher.
If your vocabulary is comparatively weak or average, then you should start off with Word Power Made Easy by Norman. This will establish a sound foundation before you move on to more difficult words listed in the official GRE word lists (Barron's 333, Manhattan 1100 etc). The word lists are important, but it is more important to practice GRE questions on your own and learning words as you come across them by understanding their usage in sentences.
The only way to improve Verbal Reasoning scores is through practice. The best book for practice problems is the Manhattan Prep 5 lb book of GRE Practice Problems.
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