It took a long while for me to start thinking about shorts, because I’ve always liked longer stories. You can “show” more, and back when I started writing I was all about subplots and action. But the market looks likes it’s moving.
Short stories for the new markets. Not flash, but 20-40k. Difficult to write because the focus is different. You have to pick your structure as you start your story, and I don’t mean “structure” like in acts, or turning points, but “time frame”. How long, in actual passing story time, does your story last? The room to explore a character arc is built into full, whereas in a short story, the character is further along, the arc is more abrupt, or the story ends on the implication the arc is completed later.
In other words? A 7500 word story, which is about 30 pages, shouldn’t take place over two decades because to get it down to 7500 words you’d need to synopsize or “tell” it. The same with multi-generational sagas that take place on two continents or in a paranormal short, include the creation of a reluctant vampire, the vampire parent’s ambition to take over the word and the vigilante group out to destroy him. They aren't as effective as short time periods. And if they include a time lapse, should have a reason for the two “pieces” to go together. It shouldn’t be part A and part D, but part A and part B, separated by a time lapse that is important so part B can happen.
If the hero and heroine part, time passes, and they meet again a week later, it’d be stronger to create a reason for one of them to take action as they part the first time.
If John and Maggie argue, Maggie storms out and they discuss the situation a week later, the story fizzles. But if John and Maggie argue, Maggie storms out, John listens to her car start, realizes he can’t live without her and does something to bring them back together right then and there, that leads up to a nicely wrapped story that ends when it should, maintains nice tension and “shows” the growth of the relationship for that space of time. Although--like in a longer story--John should be one way at the beginning of the story and different at the end. He’s got to have an arc, or she's got to have an arc, no matter how small. Taking it as a given something keeps them apart.
It’s slice-of-life, but it’s appropriate for that word count.
A longer word count can sustain more story. From your “core” story event, in this case the argument, you can either push back, or go forward from the core event and give them complications.
If John is afraid of deep water and Maggie isn’t, and their core event is that Maggie is a world-class swimmer, competes at the Olympic level and wants John to join her so they can spend more time together, then in a shorter story you’d start with that argument and move on from there.
If John rushes out of his apartment, down the stairs and trips on the last one (because he’s a klutz) Maggie stops her car to watch him, then slowly (against her better judgment) goes over to help. He reaches up to hold on to her, they talk, she tries to get away, he tries to stop her, and they end up sitting on the bottom step as the day turns to night and the stars come out? Once the emotions are in place, it becomes word count. The quantity of events don't matter. The intensity does.
That’s why the time frame is so short. If you expand it in a 40k story, then the argument is the point where everything builds to a head, then the shorter story happens. How many events you add and how far back you go depends on how much space you have. If you want to start with the argument and go forward, then you’d show the complications of their choice to stay together, but there would have to be another conclusion later where things build to a head.
If events and word count sync, it should naturally become three acts. Subplots, secondaries, random life questions and soapboxes should be downplayed to keep the focus on what’s happening between the hero and heroine. Opening with the grandmother, shifting pov to a neighbor, inserting non-humorous asides and superfluous descriptions don’t work. Every word counts.