A common error is ignoring the relationships between the characters. They should interact in ways that make sense based on who they are. For example, if two characters are siblings, their interactions should reflect that. Another mistake is starting the story too slowly. With a short story, you need to engage the reader quickly. And don't forget about the character arcs. If a character is supposed to change, make sure it's a believable and well - developed change.
One mistake is not developing the characters enough. Just having a list isn't enough; you need to give them depth. Another is having too many characters in a short story. It can get confusing for the reader. Also, making the characters' actions inconsistent with their personalities. If a character is supposed to be kind, they shouldn't suddenly act mean without a good reason.
One big mistake is having characters that are all the same or too similar. Each character should be distinct. Also, not using the characters to drive the plot. The story should happen because of what the characters do, not the other way around. And avoid introducing characters late in the story without proper build - up. This can make the reader feel like they've missed something important. Plus, be careful not to make the characters' dialogues too dull or unrealistic.