Writers have strengths and weaknesses, and sometimes I feel like I have most of the latter. Often I find myself in the trench of "showing" the story to a reader, describing expressions, hinting at the setting, and trying to characterize through dialogue so much that I forget that there is a virtually untouched area for writers, and that is using the background atmosphere to enhance the characters and plot.
The atmosphere of the setting can be used in two basic ways: to create harmony or to create conflict. Basically, the atmosphere should reflect and effect the theme.
One of the best examples I can use for the use of harmony is Kate Chopin's "The Story of an Hour". It is the story of a woman who surmises that her husband is killed in a train accident who then goes to her room to contemplate the freedom that she now feels since he has passed. Look at the following passage:
She could see in the open square before her house the tops of trees that were all aquiver with the new spring life. The delicious breath of rain was in the air. In the street below a peddler was crying his wares. The notes of a distant song which some one was singing reached her faintly, and countless sparrows were twittering in the eaves.
There were patches of blue sky showing here and there through the clouds that had met and piled one above the other in the west facing her window.
In this scene, Mrs. Mallard is thinking about being "free" from the dominance of her husband, and the surroundings themselves are "all aquiver with the new spring life". She uses the adjective "delicious" when writing about the rain which in literature is usually cleansing something. This is a perfect example of a writer's use of setting to harmonize with the mind of a character.
During the whole of a dull, dark, and soundless day in the autumn of the year, when the clouds hung oppressively low in the heavens, I had been passing alone, on horseback, through a singularly dreary tract of country ; and at length found myself, as the shades of the evening drew on, within view of the melancholy House of Usher. I know not how it was - but, with the first glimpse of the building, a sense of insufferable gloom pervaded my spirit. I say insufferable ; for the feeling was unrelieved by any of that half-pleasurable, because poetic, sentiment, with which the mind usually receives even the sternest natural images of the desolate or terrible.
Where to begin? Look at Poe's use of descriptors to set up a dismal atmosphere: dull, dark, soundless, oppressively, low, alone, dreary, shades, melancholy, insufferable, gloom, pervaded, unrelieved, half-pleasurable, sternest, desolate, terrible...And that was only in the first few sentences! This sets up a terrible conflict with not just the House of Usher, but with the very environment in which our hero finds himself.
If only we could write with this in mind. Usually this kind of thing comes not with the first draft but after probably the fourth or fifth draft. If we feel that a text is too weak or lacks that certain flare that is needed, or if the scene is rather dully moving along, throw in some atmosphere to spice it up and to help drive along the thematic nature of that text. Your reader may never notice it, but these words have a subconscious effect on a reader that is sometimes mind-blowing.