I think feedback cycles and compounding effort are important.

Feedback meaning you have definitive endings (post it, journal it, etc) to your period of “doing stuff”. Cycles meaning you repeat this over time.

Compounding effort meaning that “doing stuff” in one cycle lets you do new or more complicated things in the next cycle.

Motivation is often just the momentum you get from succeeding. For independent work, you can define your own success criteria. The methods above are helpful for feeling successful.