Lots of good note-taking recommendations here. I'll add on that for the next step--memorization--spaced repetition systems like Anki are very useful. Go back through your notes, create flashcards, and then review daily whichever ones your SRS system tells you its time to review. I've found it immensely useful for committing things to memory. Saves both time and cognitive overhead when you don't have to stop work to look things up nearly as much.