If you're able to make a living doing nothing but writing, congratulations, you lucky bastard! Know that you are hated, envied, and admired. Mostly admired.
If, however, you're like most of us, you're trying to juggle a day job, family, friends, and that demanding mistress/child/Frankenstein's monster called writing. Ass in Seat, the established authors will tell you, is how you get your writing done, and rightly so. Sit down and write: none of the "magic bullet" writing tips you'll ever hear can match this sage advice in simplicity and effectiveness. No matter how brilliant you are, if you don't finish your masterpiece, you're just another author wannabe, with a couple chapters of a novel moldering in a trunk somewhere, dying a lonely death.
But saying you're going to sit your ass in a seat somewhere and write is easy. Doing it, though...well, that's a whole other thing, isn't it?
So how do you do it? Stephen King purportedly writes about 10 pages a day, when he's writing. Which is apparently all. the. freaking. time. But Stephen King makes obscene amounts of money to do nothing but write. You ain't got it like that, right?
Yeah, me neither.
But Stephen King had to start somewhere, didn't he? He sat his ass in a seat, and he wrote until he became a household name. You may not reach those heights. Few writers do. But you can give it the old college try, as they say.
So, how do you maximize that AIS time you so desperately crave? First, you must determine when you can do it. When are you free? This may need to be very liberally interpreted. Think outside the box, in other words. Maybe, instead of driving to work, you can take the bus or train. This will give you time to write while you travel. You'll get some work done, and miss the stress of just sitting in traffic!
If you have a lunch break at work, you've got some time to write a little there. And when you get home, determine when your writing time is, and make sure that everyone else knows it, as well. And, of course, there are weekends. Every good thing requires sacrifice to achieve, okay?
The point is, do whatever it takes to get your ass in that seat as often, and for as long as you can. Accept no excuses from yourself. You may not have the time of day to write as prolifically as some, but if you work at it, you can find enough time to write something. Remember: if you only write 1 page a day, in 1 year, you'll have your novel.
So what are you waiting for? Get cracking!