Making study notes

I have been puzzling for quite a while on how to best make notes in a way that they are productive, i.e. help in getting a better understanding of the topic, as well as reusable.

A while back I came to the idea of building a linked repository of definitions and theorems in a Personal Brain database ( plex ). Although I will be using PB whenever I can, building a repository is not what it will be. As an activity of understanding the topic it may be effective but not efficient. - I have read, seen and heard it all over the place: what really makes you understand mathematics is 1: doing exercises, 2: teaching mathematics. Although I am not a teacher, thus have no students, I can pretend as such and prepare lectures. The lecture notes and slides become the end product, they are reusable and the math presented is well understood by me. It's an idea, worth trying.

I have been a tiny bit, actually. It suddenly daunts that you can choose the format of the theorem, fonts, Greek letters, symbols used, etc. But most of all, I can present it in the most beautiful and clear way I think is possible. - ( I am currently writing a technical note on Group Actions ). M208 stuff, I know, but it will return in M336.