Two things that have helped forced me to get writing done are external deadlines and writing partners. The former are often set by the latter.
I was supposed to finish my first draft by my birthday this year, so I am...very early.
I wrote 63% of it this year, slow and steady, with a target wordcount each day and a tracker to keep me motivated. Some days I went for glory and exceeded my goal like hell; only a few days I had to settle for less.
The first 37% was mostly written in a couple marathon sessions at the Writing Excuses Retreat and then over Christmas break.
I was working off an outline, and even though I did not deviate from it on a macro standpoint, I added a hell of a lot of scenes and characters and one plot twist involving two characters who weren't in the outline anyway because I sure was just making shit up as I went along. Of course I also hit a point where I'd been so concerned about moving forward that I forgot to set up a very important character moment but I just made it happen because plot and will figure out how to make it work better later.
Also there are so many continuity errors because I forgot what I had written weeks or months ago. But that is all for later too.
Everything is for later. I'm letting it sit for a month like you're supposed to. I have a solicited story to write anyway.