In the interest of full disclosure, this could turn into a "do as I say, not as I do" type of thing. This is a case where the advice I'm giving today is something that I've heard time and again, but it's advice that, while I know it's good and I should follow it, I have a hard time doing. And it all comes down to a scientific principle that I'm stealing and applying to writing, that of inertia.
You all know what inertia is, right? To put it simply (perhaps overly so), inertia is the principle that an object in motion tends to remain in motion and an object at rest tends to stay at rest unless acted upon by an outside force. While this principle governs the movement of objects in our physical world, I believe it also applies to what happens when we write. Simply put, a writer in motion tends to stay in motion. A writer at rest tends to remain at rest.
I've certainly seen this principle at work in my own writing life. For example, when I was writing Numb, I did pretty good for the first four chapters or so. I wrote every day, even if it was just a few words here or there. And then, I took a long break. If I remember correctly, I stopped writing for several months. I don't remember why anymore. I just know that I stopped writing. When I finally came back to it, I had a hard time getting going again. It took a few days before the juices really started flowing and I got into it again.
And here's the thing: I'm pretty sure when I took that break, I only intended to cool it for a day or two. But with each day that I didn't write, it became easier and easier to find excuses and reasons not to sit down and put words on paper (or into the file, as it were).
It's inertia at work. If I find the time to write every day, it's easier to keep writing. The words keep flowing, the pages get filled, and soon, the first draft is done. But if I don't write daily, it's easy to find other things to do.
That's why most authors will tell you to find time to write every day.
Some writers will set a time limit: write for an hour. Others set a wordcount target to shoot for. My advice is this: do either. Or both. Or just make sure that you get some words added to your story every day, even if it's a dozen or so.
The other trick here is to find the right time to write. I don't remember where I saw it, but I once read an article about how morning people and night owls feel more creative at different times of the day. Do some experimenting to see when you're at your best in terms of creativity and writing. And then chisel out the time every day to do some writing during that time.
I know it's not easy. Like I said, this is "do as I say, not as I do." I'm not the best at this. But I'm doing my best to live up to these words of advice.