In many ways, it comes down to the standard writing adage of "know your audience". In the case of notes, that's generally a future version of yourself; knowing how you plan to use the notes in the future will inform their structure now.
My system is constantly evolving as I discover what works for me and not, but it's in a pretty good place right now. Information gets processed in several distinct stages. I start with giving the learning material my undivided attention, whether it's a book, lecture, video, or museum. Shortly afterwards, I record my thoughts and observations in a journal as unstructured prose. This is usually about 2/3 recording things that were presented and 1/3 random connections that came to mind. The important thing is only to record what I actually understand -- if there was a lot of stuff that went over my head, it's a sign that I need to revisit the source material later after I have a better grasp of the fundamentals.
During a weekly review session, I read through all of the journal entries and index them by subject in a physical card file. Each card is headed with the subject, obviously, and the card body has a reference to the journal entry, the source material, and a 1-2 sentences summary about how the journal entry relates to the subject.
At the same time, I also make flash cards to add to my Leitner box (which serves the same purpose as Anki). My goal with these isn't to remember everything, but to keep enough of the subject fresh in my mind that I'll be able to think of the correct subject headings when I want to look information up in the future.
I use physical cards for these because I feel like they're a better serendipity engine than anything electronic I've tried. Whenever you're interacting with the system, you'll end up glancing at a bunch of arbitrary cards unrelated to your current task, and occasionally that'll be the trigger you need for a new idea.
One form of notes that I want to add to this is the long-term reminder. The idea comes from Chris Hadfield¹ and presumably others in the astronaut corps: once you've done the work figuring out how to reduce theory to practice, make a task-focused reference for it that gets filed away if you ever need to do that task again. The goal here is to directly record conclusions: if you are annotating a diagram of a machine, for example, indicator lights should be labelled with the corrective action to take in addition to the parameters that cause them to illuminate.
My system is constantly evolving as I discover what works for me and not, but it's in a pretty good place right now. Information gets processed in several distinct stages. I start with giving the learning material my undivided attention, whether it's a book, lecture, video, or museum. Shortly afterwards, I record my thoughts and observations in a journal as unstructured prose. This is usually about 2/3 recording things that were presented and 1/3 random connections that came to mind. The important thing is only to record what I actually understand -- if there was a lot of stuff that went over my head, it's a sign that I need to revisit the source material later after I have a better grasp of the fundamentals.
During a weekly review session, I read through all of the journal entries and index them by subject in a physical card file. Each card is headed with the subject, obviously, and the card body has a reference to the journal entry, the source material, and a 1-2 sentences summary about how the journal entry relates to the subject.
At the same time, I also make flash cards to add to my Leitner box (which serves the same purpose as Anki). My goal with these isn't to remember everything, but to keep enough of the subject fresh in my mind that I'll be able to think of the correct subject headings when I want to look information up in the future.
I use physical cards for these because I feel like they're a better serendipity engine than anything electronic I've tried. Whenever you're interacting with the system, you'll end up glancing at a bunch of arbitrary cards unrelated to your current task, and occasionally that'll be the trigger you need for a new idea.
One form of notes that I want to add to this is the long-term reminder. The idea comes from Chris Hadfield¹ and presumably others in the astronaut corps: once you've done the work figuring out how to reduce theory to practice, make a task-focused reference for it that gets filed away if you ever need to do that task again. The goal here is to directly record conclusions: if you are annotating a diagram of a machine, for example, indicator lights should be labelled with the corrective action to take in addition to the parameters that cause them to illuminate.
¹ Masterclass.com; Lesson #17