Ask someone who knows nothing about your work-in-progress to read a portion, oh, let's say about a thousand words or so. Tell him nothing about the plot, the people involved, the story's premise. Just hand off an excerpt.
Can that person picture the setting and discern the time period? Can he visualize your characters, get a feel for their personalities, their ages, their physical appearances (This one might not be exact depending upon what portion of the story you share, but your reader should be able to make reasonable guesses) and their relationships with each other?
Yes? Good job!
No? Back to the writing board...