<quote>When I am working on a book or a story I write every morning as soon after first light as possible. There is no one to disturb you and it is cool or cold and you come to your work and warm as you write. You read what you have written and, as you always stop when you know what is going to happen next, you go on from there.</quote>
http://www.theparisreview.org/interviews/4825/the-art-of-fic...
if you're stuck, then when you think of the task it will be in your mind as a bete noire, as opposed to stopping where you've just made some progress and are eager to continue - then it will always be in your mind as something great to return to and make more progress.
"Instead of taking a break in between projects and worrying about what’s next, use the end of one project to light up the next one."