#2. Do not try and do too much in your short story. Ever. An author who knows what she/he is doing can make a stunning story out of the most simple of ideas, plot points, or narrative. It is a much, much, much harder task to hit the same highs if the story is too complex. Short stories are far too often cluttered with too much of this.
Boy pursues magic horse and succeeds, bringing honor to his family, can be a beautiful tale. Boy who’s father was killed by the cheiftain that subsequently stole his mother, prompting the boy to find the soothsayer to learn how to weave the rope of command to catch the horse he’d heard about in a myth (insert gratituios flashback scene here) to return to the village and smite the usurper and retrieve his mother, thus bringing honor back to his family is A GREAT DEAL HARDER FOR YOU TO MAKE ME CARE ABOUT.
As always, though, if you make complex plots work, then they must not be too complex, right?