The most important thing you'll do today is deciding what you'll do today.
When you're in the middle of work (usually hard work, the kind of work you don't really want to be doing), you may find yourself asking "why am I doing this?". That's when doubt begins to creep in. And if you don't have a good answer to this question, you're going to lose the reason you're doing the work in the first place. And before you know it, you've given up on it and added another stone to the graveyard of good ideas.
David Goggins asks himself this question regularly. Usually while he's training for another ultramarathon. You should do the same. Tactically, when laying out your tasks for the day, absolutely. But also for the long-term stuff. Why am I running my tenth mile? Why am I visiting this piece of music again? Why am I forcing myself for that last five minutes in a 30-minute writing session?
Before setting out on anything meaningful, have a solid answer to "Why am I doing this?".