A notebook that stays useful

A useful notebook does not need an elaborate structure. Start with one place for new ideas, one place for active work, and an archive for things you want to keep. Finding an old thought should take less effort than writing it again.

Give each note a clear title. Add a little context while the idea is fresh: what you were trying to understand, which question remains open, or where the information came from. Your future self will appreciate the extra sentence.

Once a week, spend a few minutes reviewing what you collected. Keep what is useful, combine repeated ideas, and let the rest go. A small habit usually lasts longer than a perfect system.