Whether you're into the intricately complex high fantasy of The Lord of the Rings or you prefer just a dash of fantasy in your urban story setting, the possibilities and options of creating a stellar story that whisks your readers away to another time, realm, dimension, or universe are, truly, endless.
However, there are rules. Meh, nix "rules" per se, although I'm certain there are plenty of dedicated, well-read readers and writers of fantasy who would argue that there are, indeed, ironclad laws that accompany any good fantasy story. There are storytelling and worldbuilding elements your reader will expect, either based on their previous readings of fantasy or simply an unconscious expectation of the basic elements of storytelling, just with a fantasy spin.
Here, I'll detail for you some of the top elements to consider when you're building your fantasy world—or realm, dominion, universe, planet, or ecosphere—to life.
Description
I know. The dreaded "D" word most writers fear, simply because it can be downright daunting and tiresome, but arguably the most important part of world-building, and that's why I'm starting with it. A lot of writers struggle with description because there's a delicate balance that must be achieved, that perfect midway point between not nearly enough and entirely too much. Though most can agree that the aforementioned Lord of the Rings by J.R.R. Tolkien is a fantasy genre cornerstone, it gets as much flak for its lengthy descriptions as it does recognition for its compelling characters and richness of Middle Earth.
Perhaps your reader doesn't need to know the species of the trees that dot your plains, or how sewage systems run in your world. They may not need to know that the enormous tapestry hanging in the great hall of your realm was stitched together by ninety-nine tiny, needle-bearing fairies—then again, if it's important to the storyline and to your main character's journey, maybe they do. Maybe that tapestry is an important key to your hero winning the day, and the secrets they need are kept by those fairies.
Paint vivid pictures about the world your hero touches because it's a world your reader has never visited before. But don't bog down the story and your reader's imagination backpack with items they don't need and will only weigh them down on the climb up the mountainside of your story to the climax. Ever read a book that spends a great deal of time on a certain character, place, or item, and then you never read about it again? That would be considered too much unnecessary detail, and chances are, it confused or maybe even frustrated you. Both things—confusion and frustration—are things you want to avoid making your reader feel at all costs. But if you describe a certain character, place, or item and it reappears to play a pivotal part in your hero's journey, well done!
Characters
Vying for the number-one the most important component of your story are the characters in it. Who's your hero? From where do they hail? Are they rich or poor? Commoner or noble? Do they have powers and/or magic? If so, how does that affect them? What do they look like and how do they dress?
Just as important is the supporting cast. Who are your hero's friends? Are they human? What other races of creatures and beings live in this world?
Who's the villain? Is it an invading force from another realm? Another dimension? An evil, spiritual force? Don't make your villain just a cliché mustache-twirler. Give your villain some depth. Consider what your villain is fighting for as well, and why. Give them as much agency to do their Big Baddie thing as you're giving your hero to save the kingdom, the world, or even just the day.
Magic
Speaking of magic, this is a huge aspect of fantasy. It's what sets fantasy—low, high, urban—apart from other genres of fiction. Magic is, well, magical, but it comes in many different forms. Elemental magic, black magic, white magic. Consider what this might look like in your world.
Consider also the rules of this magic. Every type of magic has a cost. Perhaps that's a physical deficit to your hero or a mental one. Perhaps every time they shoot a fireball from their hands, a tiny troll explodes. Balance applies to magic in a big way, and it makes the story more interesting. If your hero can lift waggle their finger and decimate their enemy in ten seconds without breaking a sweat, what's the point of the epic journey?
Social status
All societies have a social structure and class of some sort—unless it's total anarchy! Where does your world lie, specifically the one your hero is in? Is it a fair society where the classes are about equal, or is it a kingdom, with nobility and royalty? Consider where your hero would best be placed inside the frame of their journey. Class does matter here, as it will directly influence your hero's resources.
Laws
Consider the laws that govern your story. Similar to magic having rules and a cost, the world your hero lives in should have both, as well. How is the hero being oppressed in their society, or what outside force is oppressing the society they must save? If the oppression is occurring within the society, what are the laws that are holding the hero down or back? How does it affect everyday life?
Geography
Where does your hero live? Where does the story take place? What's the climate like there? It could be as small as a palace, or as big as an entire world. However, keep in mind that if the story is set in one kingdom inside a large world, and only that one kingdom, describing the rest of the world doesn't really serve the story if it doesn't influence the hero's journey. Remember that metaphor from earlier about not weighing down your reader's imagination backpack during their trek up the mountainside of your story? Sure, it might be interesting for the reader to know that there's a land of ice to the north, a desert to the south, and water on both sides, but unless those are places your character will visit as part of their journey, it's probably okay not to spend more than a few sentences at most mentioning them.
The opposite is true, as well. If your character is going to embark on an epic journey across the entire land to accomplish their goal, describe each place in rich detail as long as it keeps the plot moving forward. How does the world you've created differ depending on where you are? Is the whole world hot and sandy, or are there varying climates? Let your reader smell the smells, see the sights, feel the tactile elements.
Weaponry
What's an epic fantasy story without some epic battles? Might still be a good story, but it could be a great story if you add some of those where they work and where they propel the narrative forward. How are battles fought? With magic, weapons, or both? What do those weapons look like? History is a great way to design your weapons. You can take directly from history, or you can use weapons like swords, maces, clubs, battering rams, to expand upon and tweak until you've created something totally unique.
Religion
It is entirely possible that your hero may live in an atheistic society, but most societies have a higher power they believe in. Is your society monotheistic or polytheistic? What kinds of gods or god does the religion have? Is it more spiritual, or are there rituals that need to be observed? What are church services like?
Most importantly, how does or doesn't religion influence your hero? Do they struggle with fighting battles because killing is against their beliefs, or do they revel in it, knowing their god has promised glory of some sort? Maybe your story is about your hero finding their relationship with a god or gods. While you don't need to try to model descriptions of your story's religion on the book of Genesis, it's probably a good idea to decide up front how much or how little you'd like it to influence your world, and go from there.
History
History influences how a society, kingdom, or world perseveres or fails. History precedes the start of every story unless you're writing about the creation of a certain world. But most fantasy stories take place in lands that have long been established. So what happened before the story opens? This, like every other aspect of world-building, needs to be handled with care and balance. Consider your hero's journey, and their ultimate goal (which they may not be aware of at the very start of the story). Consider their starting place. How has or how could history influence this journey? How does it affect other aspects of the story? You should avoid a long, drawn-out history lesson at all costs, but pepper in aspects and nuggets of history where they fit and where they're appropriate.