Lots of great advice in this thread so let me offer a complementary approach: when you find yourself feeling reluctant to work on the project, sit with that feeling and ask yourself where the sensation is coming from (and it might not be obvious at first—a therapist would be able to help you untangle the feelings).

In my case I learned I have a fear of failure. Once all the “easy” parts are done, and I don’t know quite how to do the next step, I start feeling uncomfortable. Not continuing is safe, because I don’t have to find out whether I will be successful. Learning new things usually requires trying and failing, and failing is uncomfortable, and our body is doing its best to keep us feeling safe.

I’ve used most of the other suggestions in this thread and they do work to varying degrees. But my TLDR advice is that these strategies are often coping mechanisms for some underlying lizard brain emotion going on. If you can gain some self-awareness about that emotion then you will gain power over it, be able to soothe it, and thus be less reliant on an external strategy.