I take notes a lot, tending to pencil and notebooks. But not only do I think there's a better way to organize things (I know I should be using a note-taking app or something that deposits to Dropbox, for example), I'm not happy with the actual things that I write down. I go back and read things, and while I can follow a general train of thought, things that seemed superfluous or too detailed at the time are now essential for context.

Where can I learn to do a better job of figuring out what to write down, and keeping it in such a way that I become a resource for myself?