For the first year of my preparation, I memorised formulas without understanding where they came from. It worked until questions were framed differently than I expected, and then everything fell apart.
The turning point was Time, Speed and Distance. I had memorised the average speed formula but didn't understand why it wasn't just a simple average of two speeds. Once I worked through the logic myself, I could apply the same reasoning to any variation of the question, not just the exact version I had memorised.
I started doing this across every topic: deriving formulas instead of memorising them, and asking "why" before "how." It slowed me down initially, but within a few months my accuracy on unfamiliar question patterns improved dramatically.
Rote learning gets you through familiar questions. Understanding gets you through the ones you've never seen before — and exams are full of those.