I've had a lot of to-do lists over the years. They helped me achieve quite a bit of things, but not always the right things, and certainly not always in the most effective manner.
Looking back, there was one chore that I should have put on every list and saved time for every day.
That missing item was "Thinking."
I mean serious, not off-the-cuff, thinking where time is dedicated, assumptions are examined, unknown subjects are identified, plans are challenged, and conclusions are at least tentatively reached. This need not be done on a mountaintop, but it should be done.
And I can attest to one thing: it does not occur automatically. You have to approach it with care and attention.