I don't like giving advice to writers because I don't necessarily consider myself an expert on anything. When it comes to writing, I kind of feel just as lost as always. But there's one thing I am good at and that's meeting deadlines.
The number one barrier most authors face is finishing the damn book. They come up with all kinds of excuses. The book sucked, they had a better idea, Lost was on. But it usually boils down to an inability to get your butt in the chair and write.
What works best for me setting goals. Like giving yourself 8 weeks to finish a first draft. I should note here that when you set your goal, you need to be realistic. For me, 8 weeks is a totally realistic deadline. I write 6 days a week for a minimum of 2 hours. That gives me 48 days of writing. If my book is 60k to 70k words, that means I have to average between 1250 to 1450 words per day. By breaking it down like that, I take the sting out of it. Thinking about writing 70k words is painful but 1250 is totally doable. Your schedule might be different so you should adjust accordingly. If you can only write 3 days a week for an hour a day, then be honest about that. But find the time to do it. My agent told me about a friend of his who writes exclusively on his lunch break.
But it's not enough to just set a goal. You have to be accountable. People do it in different ways. They tell their friends, they talk it up on twitter, they challenge each other. I do it with a spreadsheet. I keep a daily log of my word count. Then at the bottom, I have a countdown to the number of days I have left, the number of words I have left, and how many words per day I have to average to meet my goal. That last number is important because it goes up or down depending on my output. If I have a bad couple of days where I don't write much or I don't write at all, that average goes up. It keeps me accountable. It says, "Okay, you screwed up, but here's how many words you have to write per day to catch up." I've got a huge sense of self-guilt, so when I fail to meet my "goal," I feel really crappy and use that to surge ahead.
An unintended positive consequence to getting into a habit like this is that it enable you to be able to visualize later on how quickly you can complete a project. Take the book I'm working on now. When I began, I intuitively knew it would be around 70k words. I set myself a deadline of January 15. I'd started around the holidays and had forgotten to take into account the number of days I wouldn't be able to write, so I extended my deadline to Feb 1. I finished the book yesterday with a word count of 67500.
I feel like I'm rambling here. But if there's one thing I can impart it's the importance of deadlines. You don't have to tell anyone about them, if you're worried about being embarrassed for not meeting them. The only person you really need to be accountable to is yourself. But setting deadlines and really trying to stick to them, can be a great motivator to do the one thing most unpublished authors are unable to do: finish that book.