Effective description uses words to transfer a mental image from the writer's mind to the reader's. The keys to effective description are concrete words, figurative language, simile or analogy, and an orderly sequence. (See also image/imagery.)
In the following paragraph, Mark Twain uses most of these strategies to describe the Mississippi when he was a cub pilot.
I still keep in mind a certain wonderful sunset which I witnessed when steam- boating was new to me. A broad expanse of the river was turned to blood; in the middle distance the red hue brightened into gold, through which a solitary log came floating, black and conspicuous; in one place a long, slanting mark lay sparkling upon the water; in another the surface was broken by boiling, tumbling rings, that were as many-tinted as an opal; where the ruddy flush was faintest, was a smooth spot that was covered with graceful circles and radiating lines, ever so delicately traced; the shore on our left was densely wooded, and the sombre shadow that fell from this forest was broken in places by a long ruffled trail that shone like silver; and high above the forest wall a clean-stemmed dead tree waved a single leafy bough that glowed like a flame in the unobstructed splendor that was flowing from the sun. — Old Times on the Mississippi
