Perfect Short Story
The Basic
A short story is, by definition - short. But, It is a full story, complete in itself. It is not a chapter of a longer work, nor a fragment. It is not unfinished. With the last word, there is nothing more that needs to be said.
Every successful short story writer gives the same advice; Make Every Word Count.
Any word that can be removed, is removed until the next eviction would lose clarity.
Every character has to have a purpose. If the purpose is a facilitation, the character needs no name, no real back story. If there is a 'sniper' or a 'fireman' or a 'reporter', they don't need a name and credentials, just the action.
One doesn't list items in a short story. Catch-all pronouns do the duty. One example/ description is sufficient.
Unless a bottle of shampoo figures in the plot, one doesn't need to mention it. If there is some data the reader needs, this can be transmitted via a character in one of the many devices; i.e. reading a placard, overhearing, being told or describing something the narrator is seeing;
"The bicyclist was hit by the blue ford, which didn't stop."
There doesn't need to be much back story as to where and when and who, unless that is crucial to the plot.
For example; "I recognised the car, it belonged to my ex-wife', if the purpose of the story is the protagonist deciding to visit his ex-wife, or to have a quick reflection on why the marriage ended, or whether or not he would be a witness.
Editing; Vital
Although you may write a story thinking you've cut your words to the very bone, you'll find your work has just begun.
When you have completed your story, leave it for a little while. Then return with a hatchet.
You're there not just to do the spelling/grammar thing, but to cut off every single word that is unnecessary. Every incident, every character.
Your short story might have been 1700 words when you completed, it should be slightly over 1200 when you're done editing.
If you're new to writing short stories the number of words might seem far too small.
But when you recognize that a short story is to get to the point as quickly as possible, you chop off the diversions.
You don't need the long description unless it is vital to the story. If it is just to decorate, it can be removed.
You don't need to paint a picture when all that is needed is a sketch.
Short vs Short
A basic short story should be under one thousand words, consider two pages in a magazine.
One of the problems is to know when you've come to the end. Determining the end might be the difficulty.
Often an author doesn't want to let go of a character or feels the need to explain, and what was to be a short story now becomes a long chapter in a book.
If your story is about the protagonist getting/losing, the moment that happens, the last sentence is written.
Whatever the purpose, when you hit it, you're done.
Sometimes you reread it and realize you never made it clear that this was important to the character, or a major point was left out.
That means you go back to where this should be, alter what you wrote to take in the new bits, not just add them.
Get to the Point
Every good short story gets to the point. I doesn't take the long way around. It gives enough to set the scene. Most short stories start in the 'middle';
"I got off the subway at 42nd Street just before rush hour.." gives the place, the time, and there need be no more reference to where the story is taking place.
The last sentence, at the conclusion of the action could be; "The good thing about subways, they run all night."
Hence the manner in which the protagonist used to reach the location of the action was not simply a 'setting' but connects to the ending. The subway is part of the story, not an unnecessary description.
In good short stories, that connecting of the first and last sentence is the goal.