Short chapters (for the same reason.)
Never dwell on how big the total project is. Make it a series of small goals: One chapter a day, for instance. Break it down into things that can be done at one sitting, so that every time you get up, you've got something done.
My routine when going full bore was to get up, eat (because this is hard work and burns energy) and then review the just-done chapter from the day before. That reveals rough spots and holes you missed. It also primes the pump for the next chapter, and the writing on that begins as soon as the editing is done on the last chapter.
Do have a general outline for the total work, but don't hesitate to change direction. Sometimes, and this is when it gets great, your characters do things that surprise you and produce a better story. It's your own brain working at some undetected level, of course, but it's still fun. Do leave that outline out where you can see it, and when your done with a chapter, check if off so your progress is visible (otherwise you'll conceptualize and agonize that you're not getting anywhere). And give yourself a reward, even if it's just a bowl of ice cream. And then, of course, go to your day job. :-)
One other trick might help. I got badly bogged down in one book, but one night the penultimate chapter came into my head, the climax of all the plots and concepts and story lines and whatnot, it rang like a bell. So I got up and wrote that chapter just about as if it were a stand-alone short story. It was both intellectually and emotionally fulfilling to read it - a signal to me that I'd nailed the "feeling" part of this, which is always a struggle -- and it became a motivator to me to then fill in all the intervening action between where I was bogged down and where I needed to go to incorporate that very satisfying passage.
Your mileage may vary. :-)