@Fuyumiya Unfortunately, I can’t be of much help, since I rarely take notes. I mostly work through textbook problems and exams to get a feel for how different problems should be solved. For certain specific problems or hard-to-grasp theorems, I usually jot down notes in the margins or at the end of the textbook chapter about the steps to solve or prove them -- so even if I don’t fully understand them, at least I know why they should be correct, and how to try them out when needed.

@Fuyumiya
I tell my students to get one of those books with index tabs down the side of a page, that people used for phone numbers originally, but still available, then put your notes in there against a relevant tab, like Trig under "T", Index Laws under "I", etc.