The Thing about Fantasy is, you’re just making stuff up. Sort of. But not really.
I’ve touched before on needing emotional connection points in fiction: a way for readers to empathize with your characters. But it’s more than that. You have to know a bit of how the real world works if you’re going to break the rules well, if you want to build up a world that is internally consistent. Fantasy is a flower that blooms out of the same soil as any other story. It needs nutrients, it needs good clean earth. It needs to be real, and in order for that to happen, you have to feed it real things.
So maybe that garden by the enchanted palace is based on that time the author went to the gardens at the palace of Versailles. Maybe the conversation that two grizzled wizards (grizzards?) have on their sun-drenched porch is a conversation the author heard their grandparents share on their own sun-drenched porch: the sort of well-worn back-and-forth that’s been had many times over the course of decades. Maybe the way the prince tilts his head and presses one finger against his cheek when he’s thinking is the same habit shared by the author’s boyfriend. Maybe the birds that sing in Elfland are the same that sing outside my window.
It helps to draw from your own experience, if you can. We can’t all up and learn how to forge armor or ride a horse or pilot a rocket ship, but if you want to describe a field, think of the fields you yourself have seen, and go from there. Build your descriptions from that, instead of relying on other authors’ descriptions of fields. Copies of copies degrade over time. But there is plenty in your life you can draw from, if you learn to pay attention to your experiences.
What flowers did you find there? How did it smell in the heat of summer? What sounds buzzed through the air? How did the ground feel after a long rain? What was it like when the frost covered the tips of winter-dry grasses? Did their stalks crackle sharply beneath your boots?
Building a fictional world can start with broad strokes: a city made of gold, aliens made of light, people riding telepathic dragons. But as you zoom in, the world will be made real in the creak of leather and the warm smell of a bakery and a shock of green grass in the middle of a gray city. Call it verisimilitude, if you like. Build your city to music, build your world from magic, but also remember to build it in wildflowers.