Heidi Pitlor, editor of The Best American Short Stories, shares some of her experiences reading thousands of short stories. She explains it's often easier to say what doesn't work, but nonetheless provides a summary of what does:
Here are some things I wish I saw more frequently: humor, genre-bending, humor, risk-taking, a more direct addressing of real world matters, humor.
Here are some things I'm always glad to read: loathsome, despicable characters (who says we readers all crave likable characters?); bone-scraping emotional honesty; a strange, off-kilter voice; unreliable narrators; surprise; a solid command of language; a story written with urgency and profundity; great, weird titles (titles matter); the assigning of language to something I have never thought about but should have. Humor.
There's some worthwhile insights here, so do read the full post if you like your short fiction: http://www.huffingtonpost.com/heidi-pitlor-/short-story-writing-advice_b_4059132.html