I recently decided to start using a physical notebook to write my todos, instead of my usual "Oh, I’ll just remember this".
I haven’t chosen any concrete system for writing the tasks down, simply writing them all over the page, wherever there’s some empty space.
Once I finish doing some task, I cross it out with this satisfactory feeling of finale.
It’s been great, as I no longer have that feeling of thinking you were supposed to do something, but you can’t quite remember what. Also, as an added benefit, I get to see how much I’m working by how much ink the pages have after all tasks get crossed out.
I’m not sure if I’ll develop some system beyond just randomly writing down stuff, but I can say that even this has been a huge improvement.
I have moved to using org-mode inside emacs. I find that it's much easier to write down new things and let ideas flow. It also has amazing tools, like org-capture, which seamlessly let's you add TODO items from whichever file I might be editing.
I have stopped using the physical notebook, although I still write down a condensed TODO list in paper if I have a lot of items that need to be done in a day, which normally stresses me out. Seeing them all written down makes it easier to process, for some reason.