Exam

Hi Sparsh,
90th percentile is not that difficult a target to achieve. Based on last year's paper, if a student had attempted ~25 questions in Verbal, ~12 in DILR and ~20 in Quant, he/she would have scored 90th percentile in each. With good preparation of fundamentals and rigorous practice, this is a very achievable target. I am going to jot down a few critical things to keep in mind while preparing.
Prepare from basics - No fancy shortcuts and gimmicks
Try to take some coaching from nearby CAT coaching centres. They will help you a lot in preparation.
Read. A. Lot.
Solve gazillion questions to build stamina and speed
Keep at it. There will be times when something else takes precedence. Grit past these times and keeping coming back to CAT preparation.
Grasp of basic arithmetic, a well-honed reading habit and lots of mocks - this combo can easily take you to 90th.
If you are preparing with any level of seriousness, shoot for 95th percentile at least. That is also a very achievable target.
Best wishes for CAT preparation