Fantastic topic to discuss - Love it!
Here is what I did, which was probably not enough in some areas and too much in others:
1. I took notes from the books I studied, so I would note the strategies and other items that I knew I would not remember.
For example, I wrote out the reading comprehension strategy and writing it out and organizing it on paper helped me to imprint it or somehow save up there for a longer period of time
2. I printed out every question from GMAT Prep and online tests that I missed (unless something I would not miss next time, which can be hard to judge)
3. Wrote out all interesting words (vocab as I am international) in a notebook. My rule was that if I encountered that word more than once, I would write it into the notebook with a definition
4. I marked every question i missed in a book to solve it (small stars next to the question made with a pencil - allowed to erase them if I knew how to solve the question a few days later/months later or allowed to put another star for the questions I got wrong twice)
In terms of organization, I had a folder/binder where everything went but it was not anything neat or pretty
I would usually review the questions I made a mistake in the following day - I would see the question (i would remember the solution still), so i would identify the issue, point the correct answer, and point my mistake (i remembered the solution and my mistake to each question i messed up).
My 2 cents - hope this helps.