I just ran across this article on Facebook about how to tell if you’re in a high fantasy novel, which is very reminiscent of the Evil Overlord List that’s been around since the inception of the Internet. It’s worth a read, including the comments which largely continue with the theme. Both the Fantasy List, and the Evil Overlord List make fun of what tend to be common tropes and clichés in fantastic literature. (TV Tropes could be considered the ultimate such list.)
It is a useful thing for a writer of any stripe to be familiar with these tropes, because one of the primary uses of these tropes and clichés is to manage the audience’s expectations. Most of what we want to do as a writer— build suspense, fear, humor, surprise— starts with leading the audience in a particular direction. Most of the better experiences we have in fiction are when we’re led one way, and the author suddenly veers off somewhere new and unexpected.
Consider the violent sociopathic villain confronted by a second-string lieutenant who has to break the news that he just failed an let the heroes escape. What if, instead of shooting the poor guy for his failure, the villain is understanding, says no one is perfect and comforts his minion by saying, “you’ll get him next time,” as the lieutenant breaks down into tears.