How do you organize your study materials? Binder? Notebooks?

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.

Taking notes (e.g., formulas, grammar rules etc.) and tracking your progress is key to avoiding going in circles. It would also help you to revise material effectively without the need to go through the book again. I would also recommend to write down new words, as bb has already suggested. I personally still haven't figured out which suggestions from books to write down. Sometimes it seems to me like a huge waste of time. Any thoughts on that?