There’s some good stuff in this Flavorwire article “20 Great Writers on Motivating Yourself To Write, No Matter What.”
The ones that resonate with me at the moment are:
First forget inspiration. Habit is more dependable. Habit will sustain you whether you’re inspired or not. Habit will help you finish and polish your stories. Inspiration won’t. Habit is persistence in practice. -Octavia Butler
The old incapacity. Interrupted my writing for barely ten days and already cast out. Once again prodigious efforts stand before me. You have to dive down, as it were, and sink more rapidly than that which sinks in advance of you. -Franz Kafka
After having developed some functional writing habits and then promptly broken them up by leaving town for a couple of weeks, I’m currently in a guilt-and-rebuilding phase.