Hi rohitgmat,

The GMAT tests a specific subset of English grammar, so you don't need to know all possible grammar rules, you just need to know the ones that the GMAT tends to test. Beyond knowing grammar, you also need to understand "style", common patterns among the answer choices, common patterns among the common WRONG answers, etc. On the GMAT, grammar is primarily a "matching game" - e.g. matching subject and verb, matching pronoun and noun, matching parallel phrases, etc., so it might help you to think in those terms.

You might find it helpful to "group" rules based around common patterns. Instead of reviewing all the rule all at once, focus on a set of verb-based rules and patterns, then parallelism, then pronouns, etc. Try doing some light review right before you take a practice CAT, so the rules should be "fresh" in your mind.

GMAT assassins aren't born, they're made,
Rich