The other day I found myself struggling to push forward on one of the books I was writing. I realized that, in part, it was because I wasn't all that excited about it. I searched through my Rolodex of ideas and came upon one I hadn't completed but was really excited about, my animation screenplay, Sheepish. I had played around with ideas for it, but I never pushed forward on it. I think I believed it would never come to be and that since I couldn't really publish it, it wouldn't end up helping to increase my income. Unsurprisingly though, I cranked out 2,000 words on that sucker within an hour and a half today. If you can pick a passion project to write on, you will be much more likely to get your writing goals completed. Love what you're doing or start writing something you love. That's the best way around writer's block I can think of :).
I also wrote a blog post today about diversifying your goals.