Dave's post and Rowena's comment reminded me of the constant struggle to protect my writing time. It's so easy and so common for others to take for granted that if a writer is at home all day, s/he must also be available all day, to gossip, run errands, etc. People who are used to the cultural norm of the "day job" tend to forget that for a writer, writing is a job and requires time and attention.
I have to protect my writing time from myself, too. It's amazing how when I've hit a tough patch on the WIP, suddenly housework becomes very appealing. Or I have to update my blog. Or, or, or...
So here are a few tips for protecting that precious writing time. Not everything works for everyone, but this may give you some ideas.
My friends know that when I'm writing, I ignore the phone. I let them know when I usually write, and they call at other times of day, or better yet send me email that I can answer when I'm ready to connect to the Internet.
Speaking of that the World's Worst Waster-of-time, I disconnect from the Web when I'm writing. I have a separate computer (laptop) and a separate chair for writing. The desk is for business. The writing chair is for writing. My incredibly patient, supportive, and understanding spouse knows that when I'm sitting in the writing chair, I don't want to be disturbed.
Planning when to write helps. I prefer as few distractions as possible, so I like to write while the spouse is away at work. I need a fairly long stretch of time, preferably a couple of hours at least, when I can work uninterrupted if I'm going to make good progress. If I'm going to have to jump up and do something in fifteen minutes, I'm probably not going to be able to concentrate on writing.
For those whose lives are especially full of outside demands, though, fifteen minutes at a time may be all they get. In this case I'd suggest considering the charming and delightful late Roger Zelazney's method of writing. He would sit down four times a day, and each time he'd write three sentences. Doesn't sound like much, but it adds up.
Roger's objective and hope was that at least one of those four times, he'd get caught up and write more. But even if twelve sentences a day—every day—is all you can manage, it adds up to a book in a surprisingly short amount of time.
Writers tend to be either tortoises (slow, steady, every-day workers) or hares (sprinters). I'm a tortoise, though I can sprint when I need to. But a technique that I've found very helpful for me is to commit to writing 500 words a day, every day, rain or shine. Some days—most days, in fact—I write more. But I've got a long streak of daily writing going and the desire to keep it going is a great incentive.
Telling others about your goal helps you keep it, too. Dean Wesley Smith is currently tracking streaks for a bunch of writers. If you're curious about that, visit Dean's "Streaks" page .
Some writers prefer not to set word count goals, but instead designate a block of time for writing, as Dave mentioned. Whatever works. Just having a plan helps a lot.