Best way of revision in CAT prep

I have noticed that I am good at learning new topics but bad at remembering them. I can study a QA topic today, solve twenty questions, and feel confident. Two weeks later, I open a similar question and suddenly cannot remember the method.

Earlier I used to think that this meant I had not understood the topic properly. Now I feel that the real issue may be revision.

I am thinking about keeping a small revision notebook where I write down formulas, common approaches, mistakes, and questions that took me too long. Every few days I would spend some time going through it and solving a few questions without looking at the solution. I also want to avoid making the notebook too large. If I write every single thing, revision itself will become another huge task.

For people who have already completed most of the CAT syllabus, how are you revising? Do you revise entire chapters or only mistakes? Do you solve old questions again or mostly use fresh questions?

I would especially like to know what people found useful during the final stages of preparation when there is less time available.