Well, I'm no Jeanette, but I have written a few short stories..and had several rejected! What I've learned: keep the story "short" between 500-6000 words. After that you're getting in "novella" territory, and might require more explanations, descriptions, etc than you really want to go through. Also, a short story is best set in as few locations as possible; concentrate the story on action, dialogue, characters in simple, central locations. You don't want to try and span the globe with dozens of people in 2500 words. Most of all, a short story is really geared towards "write what you know". A novel, or even novella, warrants research and multi-character arcs and development, whereas, I've found, a ss is more off the cuff, Most importantly though, no matter how many words/characters/whatever, write what you want to, and when YOU think it's good...it is.