Mostly it has to do with sitting down at my desk at a regular time and writing a regular amount of words—oftentimes about 1,000 words a day. No more, no less. (I find that if you stop when you know what comes next, it is easier to pick up the thread the next morning.)
But inspiration comes from all sorts of places. Lately it has been Taylor Swift's new song "Out of the Woods" (haters keep it to yourself). Other times it is a silly notion I want to work into the story, or a line, or some other thing that has stuck in my brain. You get it out by throwing it down onto the page.