Niklas Luhmann wrote over 70 books and more than 400 scholarly articles using the Zettelkasten note taking method to learn better, think better, publish more, and be more creative.
Luhmann linked his notes together. Notes are no longer just grouped together, but their connections are explicitly tracked. This creates a web of ideas.
Atomicity: Each note should contain one idea and one idea only. This makes it possible to link ideas with a laser focus.
Autonomy: Each note should be self-contained and comprehensible on its own. This allows notes to be moved, processed, separated, and concatenated independently of its neighbors. It also ensures that notes remain useful even if the original source of information disappears. Same idea as the Single-reposibility principle in programming.
Link notes: A note that is not connected to the network will be lost, will be forgotten by the Zettelkasten.
Explain why linking: Briefly explain why notes are linked for future reference.
No copy-paste: Recalling helps the brain to comprehend the information.
Sources: So the original can be read/viewed/heard again in a later stage.
No folder structure: Use tags to aid searchability and links between notes for extending the knowledge graph. All notes can be flat in one folder.
Connection notes: When linking notes that need a longer explanation why they are linked, use a new note connecting the notes.