Sometimes with writing, what matters is getting the story down. If it is too long, or too slow, it is easier to find ways to cut it back when it already exists. If you worry too much about getting it right on the first try, not only will you fail to do much writing but you will still not have a perfect version of the little writing you did do.
Instead, allow yourself to suck on the first draft. Give yourself permission to write junk. You may be surprised at the quality of what you have written but even if it is embarrassingly poor, you can still edit the suck out of it.
That's what I do with short stories.
Short story techniques
A short story, at least when I write them, follows a simple pattern.
- The setup
- The attempt
- The punchline
This is a microcosm of the three-act structure. Something happens, someone reacts, there is a result. To get there, I work backwards. What is the kicker - aka the punchline - that I will end with. Now, what is the minimum I need to make that a real kick in the shins? Right, okay, now how do I set the stage for a (mostly) innocent character to run slap bang into that?
Everything that does not answer those three questions is cruft and I can (and often, will) cut it out in service of word count or pacing.
Here are some things that help me get word counts down and pacing up
Least words needed
Adverbs, extra description, even some adjectives - they can all be cut. Anything that is not absolutely vital to the effect of the story can go.
Pull in the scope
When I plan a short story, I aim for a single scene or moment that encapsulates the essence of the narrative. Ideally, I try to imply details as I am telling this one scene. That means very selective descriptions of only the most important details.
Having the story happen in a tight time space gives it urgency and keeps people reading. Even if that is for several pages, if the engagement level of the story is demanding enough, people feel compelled to keep reading.
I do not always get it right, which is why I use beta-readers. If they look bored or confused I know I need to make changes.
Cutting excess characters
Many of my shortest stories have exactly two characters. That's just enough for my "victim" to have someone to speak to as well as providing a voice with a different opinion.
Cut all sub-plots
Every short story that I had sub-plots for either needed to be a novella or needed to be cut further.
I like to take the shortest route from setup to payoff.
Show rather than tell
If at all possible, I try to show or imply every detail through what the character does and says. That way, I do not have to stop the action to explain anything and can move the plot forward even as the reader learns stuff about the setting and characters.
I must admit that I do not always do this as well as I would like but when I get it right, I find I have packed a lot of story into very few words.
Edit: For further reading, I highly recommend several answers to this question (including my own).