"Once upon a time when the world was young there was a Martian named Smith...an intelligent creature with the genes and ancestry of a man, but he is not a man. He's more a Martian than a man. Until we came along he had never laid eyes on a human being..."
"This is a story of long ago..."
"Many ages ago, when this ancient planet was not quite so ancient, long before man recorded his history, it was the time of Middle Earth; when man shared his days with elves, dwarves, wizards, goblins, dragons...and hobbits."
— The Hobbit (1977 animated version)
"A long time ago in a galaxy far, far away..."
— The Star Wars saga
"It was the dawn of the Third Age of Mankind, ten years after the Earth-Minbari war. The Babylon Project was a dream given form. It's goal: to prevent another war by creating a place where humans and aliens could work out their differences peacefully. It's a port of call, home away from home for diplomats, hustlers, entrepreneurs and wanderers...It can be a dangerous place, but it's our last, best hope for peace...The year is 2258. The name of the place is Babylon 5."
— Babylon 5 (introduction, season 1)
While it needs not be as dramatically or as plainly stated as in the preceding examples, every story will have a temporal and a spacial location. Not only is this important to the setting itself, but it will help you to more clearly define your characters and their place in the story. It's not technically a character trait, but it is important when it comes to developing and defining the character. As much as (if not more than) the genre, the where and when of your story will, in all likelihood have a powerful influence on the development of the character. In a cyclical sort of process, the story's temporal and spacial elements will also influence the development of your characters, who will in turn influence the development of your story, which may further influence your characters, and so on into infinity.
The temporal locus defines when the story is set. The spacial locus defines where the story is set. Feel free to mix and match different genres as seemingly disparate or incongruous elements—even the seemingly impossible—may be found in the same story, and may prove entertaining to both your audience and yourself...but try not to overdo it. Most stories will have aspects of at least two or three genres (sometimes more), but it's best to avoid throwing too many diametrically opposed themes into the mix together...at least until you're gained a certain amount of experience and you feel reasonably secure in your skills as a storyteller. Although it can be tempting to throw all of your ideas together on your first outing, few things will kill a story faster than an "Everything-and-the-Kitchen-Sink" approach.
Next time: Mary Sues and Self Inserts