Had a former student email me and ask for some of the suggestions I had for his class a few years back for when you've started a short story and are stuck in the middle and don't know where to go. We've all been there.
Here were my thoughts:
(1) think of where the story seems to logically be going, and DON'T DO THAT, (2) consider where readers would be happy to see it go, and DON'T DO THAT, (3) get sky-high on coffee, or good and buzzed on whiskey, and, well, DO THAT for now, (4) say, "Fuck it, this story is too hard," and DON'T DO THAT.
Here were my further, more constructive, thoughts:
Don't be afraid to write the ending that you think is too weird, too obscure, or that nobody will get. As long as it's connected to the rest of the story, it's cool. Don't underestimate your readers. You're not writing for the simplest readers, you're writing for the best readers. Here is something that has worked for me many, many times:
Write an ending that you don't understand but that looks cool image-wise and sounds like it means more than it seems. Now, connect the dots from A (beginning) to C (ending) with B: tension and action and narrative drive. How can you make this bridge?
For example, say I've started a story about an old farmer who is frustrated because his college-age son never stays around to help on summer days and always sneaks off to play tennis. I get to the middle and he's working out in the field, and I get stuck. So, I think of all the obvious stuff: son comes around and helps father more, father learns to respect that his son has other dreams, blah blah blah. Not doing those. Instead, I try to think of a powerful image. I come up with, "Farmer Krewder let his wife's words hang in the air for a moment, and then he took out his pocketknife and starting cutting the string's on Jason's tennis racket one by one. 'You're going to cut yourself,' she said. 'No,' he said. 'There's no blood here.'"
What the hell does that mean? That's what I want to find out when writing the bridge from A to C. Come to find out in this case, Farmer Krewder's wife has explained to him that his son Jason told her he is gay and cares for his tennis partner. The ending I've written seems to show that Dad is not happy or very open about this revelation. I may have to tweak the beginning and the middle some to avoid "deus ex machina" and build further tension in scenes, but the ending has meaning and is not too cliche or common, perhaps.
It's worked for me many times--writing the beginning first, the ending second, and the middle last.