Does the title of your story spark interest?
Read your story aloud ensuring that it flows from beginning to end - eliminate the stumbles.
Does your story capture the reader's attention from the beginning wanting them to read more? Ensure each and every word is a progression to your ending advancing the plot; be ruthless and remove unnecessary padding - irrelevant information that does not progress your story is not the solution to meeting a word count. Is your ending surprising yet fitting and altogether a satisfying conclusion?
Be consistent with your point of view, the tense (past or present), names, descriptions of characters (hair, eyes, clothing etc).
Check the POV used. Would your story work better if it was told in a different POV?
Do your words paint pictures in the reader's mind?
Double check the basics of grammar, spelling and punctuation.
Follow editors guidelines and meet their requirements; word count, genre, presentation and whether they prefer emails or traditional post.
Above is a short story checklist I started for myself. I hope it helps you in some way. If there are any points you can improve on or better still, add to the checklist please let me know in your comments. It's a good thing to help each other :-)