Per Brian A. Klems on July 8, 2014:
First, evaluate your daily schedule. Find at least 15 minutes of every day—that’s right, every day—to dedicate to writing. Whether it means you have to wake up 15 minutes earlier, go to bed 15 minutes later, eat lunch faster, take a notepad into the bathroom—whatever it takes, you have to make time to write. It’s the one and only definitive prerequisite to being a writer.
Another option that works for me is to set the timer for 45 minutes. Write until it goes off, get up from your computer, and take a fifteen minute break doing something completely different. You’ll return full of energy and enthusiasm. I promise.