At the beginning of a sprint, the project manager sat down for about 10 minutes and looked at all the cards in the inbox and decided if any should be moved to the backlog. He then rearranged the cards from most to least important.
This prevented the need to think at all when working on the project - I just took the top card from the backlog and put it into in progress until it was done.
I realized, why don't I do this for my own projects too? Since my own projects aren't paid, I for some reason think they should just be able to be done without organization. I've implemented this same system in Trello for arbitrary projects and it seems to work well when I use it. Also nice that it makes it easy to collaborate if relevant but that isn't required.
It's a hard problem though - figuring out how to "Just Get Things DoneTM" is a skill that requires trial and error to figure out what you'll actually stick to, but in some ways is the most important thing to figure out.
I also highly recommend the book The One Thing - my coach recommended it to me and though it started a little fluffy the second and third sections were solid. In short, doing less helps a lot.
The Twelve Week Year is another book with some good ideas - instead of planning long into the future, plan only on a quarterly basis, and have that quarter align with your grand vision for the future.
Happy to chat more about this, as it's a problem I've wrasseled with a lot too as a self-employed freelancer. My email's in my profile.