I have this cycle I go through. Usually it starts with having a great idea, either for a new story or for an ongoing draft, jumping on the Muse's bandwagon and careening along joyously for a while. At a certain point, though, I find the momentum of any single idea starts to peter out, and I then go about looking for another solution to a story problem, another form of inspiration, to carry me further forward. It's often a good idea if I'm losing momentum on one story to jump to another for a little while - that too can preserve my overall sense of forward motion and drive as a writer.
Then eventually I hit a point where I'm low on momentum for all my stories. This could be because I'm exhausted, or having energy drawn off my writing by other commitments, or simply because I've got one story problem here, one there, etc. across the board. So at that point I ask myself, "What should I do?"
I reassess my trajectory.
This is amusing inasmuch as it closely resembles the process of evaluating story trajectories - in fact, the story in question is my writing career. I go back to the file where I keep a list of all my finished and ongoing projects. I check to see how many pieces are out on submission, and where. I also check how many pieces are in progress, and how far along they are. Then I look at where I should be putting the most effort in the context of the current state of affairs in my writing - to put it another way, where I should be looking for inspiration.
The state of affairs changes, and my priorities change accordingly.
Back when I had no publications at all (which doesn't seem that long ago), I had ongoing novels and short stories and had to make sure to keep some attention on each side because I didn't know which one was going to break first - but in 2006 I took some of my efforts off fiction for a while and put together a nonfiction piece about point of view. This turned out to be a good move, because I had the piece published in the Internet Review of Science Fiction, and got a really good response from readers. One of the other effects of that piece was to make me feel more confident that I was capable of doing something other people would want to see (fiction or not!).
My first short story publication changed things a lot. I knew I had to keep writing novels because that was something I wanted to do in the long run, and short stories wouldn't necessarily help me move toward that goal. However, when "Let the Word Take Me" sold I realized I was going to be doing both shorts and novels for quite a while, and I made it my goal to try to do another linguistic/cultural alien tale for Analog. The result was several months of intense concentration that culminated in "Cold Words." That story's reception in turn reminded me that I have to keep this linguistic/cultural short story thing going. And I'm doing my best - "At Cross Purposes" has landed and will be coming out toward the end of this year.
Based on this you can easily imagine I was pouring most of my efforts into short stories for a good while - not because I prefer them (I like both lengths for different reasons) but because I felt that was where I could make the biggest visible difference in getting my name out as an author. Once I had a story submitted to Analog I used the lull of waiting for response to turn around and put a bunch of effort into getting my novel, "Through This Gate," submission-ready. This resulted in another period of intense effort that eventually led to my signing with the Grayson Agency in October of last year.
At this point, I have abundant reasons to continue pushing both on the novel front and on the short story front - but things look a little different, too, because I can identify another goal, that of getting published in the fantasy short story arena. Needless to say, no matter how much success you have, there's always another opportunity out there to strive for.
The point I'd like to make to other writers is this: it is a very good idea to take the time to look at your writing career from the bird's eye view, even if you only do it occasionally. Each time you reassess, try to determine whether there is a single area, even a single story, where you can concentrate your efforts for a while to achieve the maximum effect. What the maximum effect will be depends on your own current goals as a writer.
In the same way that a story is not simply made up of cool sentences, but has overall structure and drive, so does a writing career. The Muse has her uses, and she's certainly worth following, but she doesn't necessarily have a good sense of overall direction. That resides with you.