I'm about 70% through this book. I've done every exercise and have meticulously journaled about each concept as I encounter them into my Zettelkasten.
Best part: you can read it online and then determine if you want the physical book (which I prefer for math).
Those are the things that I found most helpful on my recet foray into the Zettelkasten world. Could save you some time.
One thing my notebooks don’t have is structure and a system of referral. This makes it hard to reference previous ideas and concepts. In fact, I don’t because it’s so difficult - it’s just one big stream of consciousness. And it seems Zettelkasten does that!
That other comment gave a link to that "how to take smart notes" blog post, the HN comments were here: https://news.ycombinator.com/item?id=22341518
A thing to keep in mind: there are two schools of thought. Niklas Luhmann was an extremely productive German sociologist who used his index cards system in a particular way. One school of thought tries to use his system exactly, like explained in the book that blog post is about. Others think that Luhmann had to work like that because he was restricted to physical cards, now with digital tools we can make other choices and get similar effects. Both ways are referred to as "Zettelkasten method".
I also realized that the system really works for producing content, things like producing science papers. You need to put work in how you formulate notes, and in finding connections between them. Without a good reason to keep working with your Zettelkasten, there is a risk it'll just be a pile of notes.
If it’s not possible, let me at least give you a couple of questions:
1. What app are you using? (And why not Roam / why not Obsidian?
2. What do you put on one Zettel? Just theorem? Theorem+proof? Some bigger mass of knowledge?
3. Do you rewrite the proofs in detail, or just explain them using your own words without mathematical rigor?