Many of my favorite stories start with "once upon a time..." When I made up choose-your-own-adventure stories for my brother and sister during long car trips as a kid, that's always how I'd begin.
One of my favorite fairy tale books of all time, A Norwegian collection called A Time for Trolls, takes a slightly different tack with "there was once." (Then again, that could just be the translation - perhaps the original interpretation exactly matched the English "once upon a time.")
And, of course, there's always the famous Star Wars A New Hope opener: "a long time ago in a galaxy far, far away." A seeming innocuous phrase that sends the brain spinning in loops when you really stop and think about it; with one line, the movie sets itself apart from just about any other scifi film ever made.
These various openers act as a form of cultural shorthand, triggering our collective memories to properly set the scene with only a few short words. A child with British origins, for example, will likely picture the castles and knights of her history. Images of fearsome Viking warriors will probably fill the mind of a Scandinavian barn.
The usefulness of trope openings is tempered by the necessary baggage they come with. That's why I decided to get creative. My book starts not with one of these traditional phrases, or even with a third-person view of my main character. Instead, we're introduced to the world by two minor characters engaging in dialogue about the action that is about to unfold.
It's yet to be seen whether this is effective in painting the scene for my novel. Let me know what you think!