[Question] How would you take math notes to make the most of them?

I’ve been heavily influenced by reading about the zettelkasten method (and its siblings); it seems to, theoretically, solve many problems that I (a bioinformatics student) encounter on a daily basis.

However, I’m struggling with implementing said method in practice. While in biology I think the it will be easily applicable, in math I have some trouble with both splitting the information into chunks (zettels, if you wish) and then with linking those chunks together in a meaningful and useful way.

As an illustrative example, let’s pick analysis, with the common theorem-proof-definition-proposition-proof structure (think Baby Rudin). How would you split the information, and how would you link it together?

Another problem I’m having concerns note-taking in general; especially in math I often feel I’m just copying the textbook, and that there’s no added value in my notes. What information should go in my notes, as opposed to just staying in the textbook?