One thing that I’ve found helpful is to have an understanding of the journey you’re on and what steps it will take to complete the project. Then you can start checking things off as you go, which can give you a good sense of progress. For example, when I started my project, I identified different sub-tasks like defining the characters, figuring out the basic plot, sketching the rooms, creating cover art, getting a rough prototype of the first scene, defining the NPCs, writing dialog, creating the help system, creating hints etc, getting your first external tester, writing documentation etc. There are lots of different steps, and if you’re stuck at one stage, then you might find motivation in pursuing some of the other tasks. In general, I recommend keeping the scope modest, so that the number of tasks doesn’t seem overwhelming.
I hope that’s helpful.
–Zack
z-machine-matter.com