When you read a short story, you come out a little more aware and a little more in love with the world around you. – George Saunders
Identify the core of your short story.
What is it you want your story to convey? Don’t be afraid to pick a large theme (i.e. tragic loss) but understand that in the short story genre, you will not have the ability to expound on your themes because brevity will be key. Explore your intentions and then stick to the core of your story.
Set up your main characters and their details right away.
When meeting the goal of a short story (Usually 3500 words or less), the writer needs to focus on efficiency of words to describe the event or character. As an example, if a characters profession does not play a role in their make-up for the story, then leave it out. The challenge will be to give your characters depth and a connection to your readers, while limiting the amount of words.
Edit, Edit, and when you are done, Edit again.
Of course this is a staple of all creative writing, but is even more important for the short story writer. You must always be asking yourself, “Do I need this word?” Can you use a phrase to imply the same meaning as several words? Instead of “All of John’s friends believed him to be honest and reputable” perhaps “John’s behavior was that of a boy scout”
I hope this helps either to motivate, realign your focus or just flat out inspire you to put into writing or finish a short story you are working on.