For "Followers of Torments" I added a new form of torture to my main character. I could tell if he wasn't suffering enough just by how well the story was flowing from my fingers onto the screen. When things were too easy, I would stall, struggle, and get almost no where - a paragraph, a sentence - by the end of the day. When he was actively being put through literary Hades I could see almost a full chapter emerge by the time I had to admit to being too exhausted to type coherently any longer.
Not sure how things are going to work in the next series. But, I am sure something will come along to provide signposts for me to follow about keeping things moving.