The Mechanics of World Building

One of the things that stands out as the deliminator between great fiction and mediocre fiction is the ability to build credible worlds.

 Building a credible world is more than a sweet premise, like say Vampire Ninjas who wear awesome reflective ninja suits (Ed. Sparkly Ninja Vampire Boyfriend: coming soon from Moorsgate Media).  A credible world starts from a reasonable (or not so) premise, and then builds a realistic world around that premise.  Credibility in world building comes from making the incredible credible.
 If upon reading your story or your game plot summary, your testers keep telling you "I don't understand why Ninja Vampire Lestapolizes would rebel against the Triamphumphrate of Zoldan?" then you have a credibility problem.

However, solutions to the credibility problem are easier than you think. One of the reasons that A Song of Fire and Ice is so popular is that the author has taken a fairly fantastic premise and built a credible world around that premise. Sure, dragons and ice zombies are fairly fantastic notions. However, backstabbing alliances of rich people, wars over rightful succession, and the obligations of a liberating power, are all credible everyday topics. GRRM has explained that most of his source material comes from The War of the Roses,  British civil war that took place in the 15th century. GRRM added fantastical elements to a historically supported story and wound up with a massive hit that has spawned a hit TV show and a legion of fans this is giving Tolkien a run for his money.

While not everyone's story will take off like GRRM's, there is no reason to not explore the possibility of using a historical platform to tell an ahistorical story. Human history, written and oral, is full of tales of heroes and villains and political machinations.  A story can not be hurt by researching a historical event that has parallels to the world you are building.

 Writing a zombie apocalypse story? Check our the Black Death for inspiration. What did people do when faced with the seemingly realistic proposition of the end of the world? Alien invasion? Look to the Macaque, the Sioux, the Taliban (depeding on your character's POV).

The world building process does not have to take place in a vacuum. Science Fiction is built on historical allegories, there is no reason to abandon that path. If you are finding that your world isn't credible, motivations are murky, check to history, and it might provide the future.