Focus is supposed to mean you have a clear idea of who you are and what you need to work on, and also what you don't.
So I've taken to follow a (bespoke) process where I identify what my own personal principles are, and what priorities and efforts they imply. Then, of all the "oh I could/should do this" potential tasks that occur to me, I have an out: if it doesn't align with my own personal focus, then I can delete it.