When I was writing my thesis I had one rule that kept me going: one page a day. Every day I had to add at least one page to my thesis. It could come from text or charts or a table or the bibliography or wherever, but that page count had to go up every day.
Some days, I added a paragraph that spilled over onto the first line of a new page and that was that. Other days, one page became five became 20 as I hit a rhythm. It was always about giving myself that chance to hit it off for the day.