In "No Plot? No Problem!", Chris Baty introduces the Time Finder, a tool useful for figuring out how in heaven's name you're going to find time to write a novel in a month. The Time Finder is great for NaNoWriMo, but it's a bit too powerful for establishing a regular writing schedule. If you want to choose now to whittle away all the little time-wasting activities in your life, you can go ahead and use the Time Finder as it's written. Personally I can give up leisure reading and Internet surfing for a month, but not indefinitely.
Instead, I'm going to use this tool as a kind of starting point for discovering those activities that are truly cuttable - mostly the little time-wasters that nickel and dime me out of productivity.
I filled out the Time Finder a few days last week and discovered, not entirely surprisingly, that the Internet sucks away more of my time than I intend. I've actually considered going offline during the time(s) I should be writing. Then I have to find another source of music, since I usually listen to a local classical music station over the Internet while I'm writing. It's very staticy over air, unfortunately. Still, that's doable for me. I just have to hit the discount and thrift stores and see if I can pick up some cheap classical or ambient music. I'm always bored with the music I actually own, which is why I listen to radio.
Once you find some time into which you can shoehorn a bit of writing, you need to decide on a writing goal. From experience with National Novel Writing Month I know that I can generally crank out at least 800-1000 words per hour. So I set my daily writing goal, initially, at 800 words, or one hour a day. Sounds doable. So I look at where I can carve out an hour, or perhaps a couple of half-hour sessions for writing.
Later on I'll lengthen the session or increase the target word count. Getting the habit established is my primary concern. You may have an idea of how you work as a writer and a person with things to do, so your method may vary. The point of the Time Finder is to dig a little writing niche out of the less-than-useful sections of your day. Trim out fifteen minute sessions if that's all you can manage. Some people work better in short bursts, others prefer to sit down for a while and get the day's work banged out all at once. If you don't know how best to schedule your writing, pick a session length that fits into one of the spaces you've made with the Time Finder and start with that. After a few days you'll begin to see whether you tend to sit longer and write or get antsy halfway through the session. And then you adjust accordingly.
The important thing is to sit down and write every day. This is advice which has been bandied about by writers for many years, and some disagree with it. Again, you know yourself, and if you're not sure, you'll find out once you give it a shot. It could be you work better with longer sessions less often during the week. I suppose the most important thing is to write. Whether you write every day or sequester yourself away for half a weekend, turn up at the keyboard or notebook and give your Muse a place to play. She'll be happier if you do.