1. As I'm writing, if it's in my head as a "oh, that needs to be done", I write it down. Tiny or large.
2. If it's really large, I tend to word the task as to break it up. Otherwise I'll spend a day working on that one item, which defeats the purpose of trying to give my brain dopamine/etc.
3. If at any point in code I think of those "oh, I gotta remember to fix/refactor/add that" I write it down.
It's quick because I don't need to give others context. It's short, because it's just for me and it shouldn't be too far away from my current context anyway. And finally it helps me actually take breaks, and come back getting right into it. I try to never leave without writing what I should do next.
To pair with that, I chose a todo app (Dynalist atm) that I enjoy using. It should be quick to get ideas onto paper so to say, and not bogged down with features. This is more of a notebook, than a todo.
Anyway, it's all an experiment for me. I'm on week two or so of it, and it's been great so far. Good luck if you try it :)
edit: fix stupid list formatting.
For me, a lot of times it's boredom. It's boring to have to do 2 hours of work sometime in the next week; it's far less boring to have to do 2 hours of work in the next 90 minutes.
(Note I'm not recommending this, as it's basically medicating your boredom with stress, and stress has a lot of well documented side-effects).