Most importantly, to have a set of technical drawing principles to abide by, a checklist of "Alright, hit that first; now onto this." I know I do, it's just a matter of formalizing it and "doing it to such a degree... that you're eventually not even aware of it." (The Book of Five Animation Discs.)
(The drawing of the sculpture's been floating around since November. Added the girl over the weekend.)
Am thinking one of the overarching first principles is: Sit on your work. Come back and look at it with fresh eyes.
And not to demotivate the Inktober crowd, but: Never ink or commit to your first pass. At least, not until you've practiced the former. The old sketchbooks are a testimony to this.
Anyhow, I think stepping away from the main piece and doing studies helped, whether in the margins or on a completely separate file. Given that Photoshop allows dragging and dropping between files, why stick yourself to one cramped canvas to figure something out:
(Still a bit too literal.)