Every short story hinges on a simple inspiration. Because the short story form is so brief, you don't need complicated, tangled back-stories or intersecting subplots; all you need is a sharp, clear idea that you can sum up in a sentence or two. Every headline you read and every person you pass could trigger that idea, so keep your eyes open and your mind engaged while looking for your plot and characters.
Start With Your Surroundings
Look around you and see what catches your eye. Perhaps your apartment has scuff marks running along one wall from before you moved in, or perhaps your roommate has an oversized, tattered sweater she sometimes wears. The scuff marks might lead to a story about a boy who is having trouble at school and whose parents must drag him out of the apartment one morning, his shoes leaving marks on the walls; the sweater might inspire an idea about a girl who refuses to stop wearing her boyfriend's old military jacket after he is killed in action.
Draw From Your Experiences
You don't need to invent a story from scratch; you've probably had or heard about strange experiences that you can use as a starting point. For example, your American parents might have learned that their grandparents were from the same small village in Poland, you might have attended an awkward family event with a cousin who has converted to another religion, or you might have ended a relationship and realized only later that your ex was an alcoholic. Real-life situations like these offer believable, concrete ideas for short stories.
Retell the Classics
People remember myths and other classic tales because they are good stories with human themes that are still relevant, and retelling them in a modern setting can be fun and engaging. Choose your favorite myth, put its plot points in simple terms and rewrite it as a contemporary story. For example, the story of Antigone is about a person who insists on doing what's right, even though the authority figures in her life will punish her for it. You might write about a girl who knows that a senator's son raped her friend and tell the story of what happens to her when she refuses to keep it secret.
Create a Snapshot
Not all short stories have intense conflict. Some tell gentler, subtler stories about a moment in a person's life or in human history. Imagine vintage items that may once have been important to someone or old houses that have seen generations come and go. A short story can paint a picture of the history of these things: an old woman watching her grandchild in the rocking chair that was hers when she was young, remembering her brother who used to play in it, or perhaps a family returning to their ruined ancestral home for the first time since Hurricane Katrina. Remember to give these stories a beginning, middle and end, even though they may be more about nostalgia than suspense.