So for all the stories in various states of undress, I added a new one in recent months, a collaboration urban fantasy. Since it's a collaboration, most of the work on it has been relegated to the meetings with my fellow writer. But that means I have about three to four stories currently running around in my head (four if you count one that I have completed but am not actually working on except in my head).
Now lately, my focus has been on editing Hounds, one of my urban fantasies, since the clockwork ghost story has been so tricky.
Here is my observation:
As I make progress on one, I am motivated to (and actually do!) make progress on other stories.
Although I'd been spending my free moments trying to rearrange and rewrite Hounds, as I found scenes to drop, or chapters to rewrite and combine, I had realizations about scenes and chapters for these other stories. As I edited that more, I wanted to write more, and spent more time on the bus writing the opening chapter of the collaboration...instead of listening to music and zoning out.
So my advice (as always, take with a grain of salt and "to each their own," since everyone's process differs), is that if you are stuck in one story, try switching to something else. It may help break through the block, and you can return to the first story with rejuvenation.
I don't switch from one to another every few minutes, but as I work on one, I keep the others in mind, and make notes of changes and new things that can help those others for when I do work on them, later that same day, or maybe the next.
Happy writing, everyone.