I take notes by finding common concepts among different topics and constructing a hierarchical mental model of the domain i'm taking notes on. for example, for programming languages, while there might be many dozens of languages, they all share similar components:

- data structures

    - boolean
    - array
    - hash
    - ...

- control flow

    - for
    - if
    - ...

- io

    - read/write
    - ...

I use https://dendron.so to actually take my notes. Its a markdown based, hierarchical note-taking application built on top of VSCode (disclaimer - i'm the author)