A little research suggests that world building is a huuuge part of the formula for a WotF win.  I say this based on the stories I’ve read in old anthologies, my own personal world-building peak in “Poison Inside the Walls”, and the few stories of other winners I’ve had the chance to eyeball.  (Winning has perks.)  Without divulging (or even hinting at) details, I wanted to sare some world building advice based on my observations.

1. Don’t stare at the sunset. I don’t care if there are three suns and they cause green lightning on the horizon, don’t just look at it.  The parts of the milieu (world, culture, etc. of your story) that most affect your story will be things the character interacts with.  Want to describe a door?  Walk a character through it.  Want to describe the food?  Take a bite.  Want to describe the sunset?  How does it influence your character?  Maybe it creates unfavorable glare on a monitor.  Or causes solar-powered equipment to switch to reserve power?  Describe whatever you want, but find a way to advance either the plot or the character(s) while you do it.
2. If you do stare at sunsets, make sure it’s important to the plot. If you can remove an element from the story without altering the plot structure, don’t describe it.  Or a better way to say it, the number of words used to describe something should be directly proportional to its importance to the story.  I’m working on a story with two moons.  Their relative position in the sky determines the timing of the festival the story is based on.  Still, they aren’t directly involved in the plot, just its timing.  So I mention them, but no one marvels at their beauty or anything.  If the sunset marks the moment the protagonist’s boyfriend met her AND proposed to her AND said I do AND is being put to death, maybe this warrants a few poetic words.
3. Don’t hide anything. Why should you?  The written word is a slow enough method for relaying information.  If you can fill in another piece of the puzzle early on, do it.  Once the reader knows everything, stop writing.  A story of discovery is just that, chaining discovery after discovery together for your character.  Nothing pulls a reader in better than having them feel like they understand.  Think how fast Harry Potter learns things once Hagrid shows up.  There’s always more to learn when it becomes important.
4. Spread things out. Nothing’s more boring than watching all the props set up on stage before the play starts.  Get the action going and fill in the milieu as pieces become important.  Remember #3, don’t hold things too long, but don’t dump everything at once.  In PItW, description starts with mushrooms (a little bit like a sunset, but very important to the plot in multiple ways), then it moves on to alien habits that tell strategic information about the enemy without being a dossier, then to the city, the culture, an on.  I could have started with a history lesson explaining why the warriors were women and the status of things on the moon, but why?  Move through the story with a flashlight, illuminating things when you get there.  If you aren’t going there in this story, leave it dark.  Do not be Dan Brown.
5. Embrace symbols when they occur, but don’t blueprint them. Unless you’re Hawthorne (who bores me), symbols are not likely to be the center of your story.  But they are likely very important.  The more important an item is to the story, the more symbolic it probably is.  The One Ring.  The Monolith.  A lightning-shaped scar.  The Battle Room.  If you’re familiar with these stories, you know which story I’m talking about just from each noun.  Central items that carry a world of symbolism and which the plot falls apart without.  If a lucky rabbit’s foot is your symbol, could the plot survive without it?  If it can, it’s beneath extrapolation.  Don’t go looking for symbols to describe; they’ll find you.

Most of this advice can be found other places, probably in better forms.  I just wanted to pass my observations on to you.  If you can throw a reader into a world very different from ours in a way that directly influences the plot and answer their questions as they arise without stopping story motion to do so, you can write a story that will succeed at WotF.  It still may not win, but you’ll have a lot of momentum to ride.  It’s as helpful to say that if you can jump into the air and repeatedly find a way to propel your complete body mass upward again before it comes down and without touching the ground or other solid objects, you can fly.  But having a goal.  It takes a lot of crashes before you can fly.  Keep at it, one day you’ll find you missed the ground.