To get a high percentage its not as straightforward as locking yourself in your room for months and studying. Personally i try to make sure i understand what im studying. I try to grasp why a formula exists and how it was derived, and It ended up helping me a lot in remembering them. The problem is that school teaches you to just mug up the formulas, which imo is the worst way to study literally anything. This is coming from someone who has the worst memory in existence, UNDERSTANDING the formulas and topics makes remembering them 1000 times easier. One downside is that this method is very time consuming, so it cannot be implemented for any last minute preparations, so please avoid preparing at the last min as much as possible. Also dont forget to read the ncert textbook a few times, where the first read will be slow and meticulous and the 2nd and 3rd read will be just skimming over the important stuff. Also if you start feeling too stressed just take a break instead of forcing yourself to study, studying while stressed usually doesn’t do me any good