With a novel, you can take 400 pages to veer off into details of supporting characters, build a backstory, or construct an elaborate setting. With a short story, you don’t have room for any of that; you’ve got up to 20,000 words to tell us everything we need to know about your characters, their situation, their history, their relationships, their struggle, their resolution, and why we should care.
Still, sometimes you need to overwrite
As a writer, you may need to construct events that lead up to the main action of the story. This is called overwriting, and it can be a useful and necessary approach. But this step should end up being much like the Iceberg Theory we mentioned in our Guide to Building Characters—an important developmental step that is helpful for the writer, but one the reader does not ever need to know about. So don’t be afraid to overwrite your first draft; just know that in the rewrite, you will need to retell that story with the fewest possible moves and words.
But remember: start as close to the end as possible
A short story should take off running. You want to be sure you get to the heart of the conflict quickly by starting as close to the end as possible. Now’s not the time to get flowery with language and spend a page and a half talking about the way the sun came in through the window. Get us right into the issue your main character is facing.
For example, you’ve got a story about two friends who get into a fistfight. Don’t waste the reader’s time talking about how Jimmy is fired up, how he opens and closes his car door, turns the key in the ignition, drives to the bar to confront Rod, feels the gravel underneath his feet as he’s walking to the door, arrives and says, “I heard you slept with my girlfriend, Jenny, is this true?”
Not only is the lead-up in this example tedious, obvious, and unnecessary, but the speech is unnatural. We can assume Rod knows exactly who Jimmy’s girlfriend is—he slept with her, after all!
It’s much more interesting to begin with Jimmy’s fist crashing into Rod’s face, describing the sound Rod hears when his nose cracks, the temperature of the blood running to his lips, the salty-metal taste of it.
Keep in mind that readers are very unforgiving, especially today with all the distractions of modern life. Spend too long setting up the scene where the action eventually takes place, and you'll risk the chance that we’ve already closed the book and are off doing something else.