New fiction writers usually begin with a short story. This is a wise choice since a novel requires a lot of experience and the stamina of a plow horse.
But what are the essential qualities of a short story?
Brevity is one obvious feature. A story that rambles on for several dozens of pages is likely to be considered a novella, a twilight zone genre that is unpopular among publishers today.
Two other aspects should be kept in mind: singleness of effect and a limited number of characters. A novel has the space to explore sub-plots and a mixture of diverse effects like sadness and humor. A short story must get to one point quickly with a few characters.
Realistic, pithy dialogue is important to a short story because it can serve two purposes: to advance the plot rapidly and describe the characters by the way they speak. One famous author never provides a narrative physical description of his characters. His readers form a picture of the characters based on their dialogue.
The question of what constitutes a good short story is more difficult to answer. A story can succeed in creating subtle nuances of meaning within its brief format. Good examples of this are found in J. D. Salinger's collection "Nine Stories." Seven of the stories have tantalizing endings patterned after satori, the sudden flash of insight taught by Zen.
A short story doesn't have to be plot-driven and resolve a conflict. It can be a character study or focus on mood and atmosphere or explore philosophical ideas. Some great stories are virtually plotless and leave the protagonist in confusion at the end. Simplistic moral tales are almost always boring.
W. Somerset Maugham was fond of understating the case by saying a good short story has a beginning, a middle and an end. Although Maugham wrote many good stories, this sounds more like advice for writing the stage plays that made him famous early in his career.
Which brings up a salient fact. Few successful authors are able to shed much light on exactly how they wrote their stories. Guy de Maupassant, widely considered the best short story writer in history, once composed a great story about a ball of string to win a bet. Isak Dinesen could weave a fascinating story if given a random first sentence. But neither writer was capable of teaching anyone else the secret of their story-telling magic.