Any day in which I do not make progress towards one of my Big Goals is a failure. Any day in which I do make progress is a success.
Remember this when you decide what today's todos are. Remind yourself of this when you have to juggle priorities and ditch half of your list for today because something came up. And forgive yourself for the times you fall off the wagon; shit happens. But let that little bit of "I got fuck-all done today" guilt carry over to the next morning to spur you to the Big Important Projects.
This is how I kept myself working on long projects, first one that took a year, then one that took five years. Some parts were slower than others. Some were interrupted by life.
The fewer Big Things you have to juggle, the easier it is to keep returning to them.
Use whatever todo list makes you happy. Personally I use a lightweight version of the Pomodoro method; I write down 3-5 things to do with my day on a post-it, with 4-8 checkboxes total next to them, each representing a half an hour. I usually never check all of them because Things Come Up. This post-it stays on my desk, and gets the next day's stuck on top of it. Every now and then I look at old ones and toss them.