Read your work aloud. Don’t send it out without taking this step.
This is how to hear the unintended repetition and awkward phrasing that will clang in readers’ ears—because they’ll clang in yours as well. The places where you stumble will likely be spots that will trip up readers, too.
Print the story rather than reading it from a screen (though that’s better than nothing). Have a pen or pencil in your hand and mark it as you go.
You’ll hear the mistakes that spell check won’t find, that your eyes alone can’t see. It’s the time for your ears to do their part.