Buckle up chuckle fucks...
First, you become mentally insane
Then you become sane
With me so far?
Good
We will then lay down in a bed after working on the story for a day, ask yourself what it would be like if you were put in that world. what would you do. Then as your in the limbo state between sleep and wakefulness, you let your mind explore the world.
You start to add things, sights, characters, and slowly you begin to build a world that once you fall asleep, you join. Then you have yourself a good way to write a fantasy story.
This wasn't what you wanted...
Anime. I visualize it like stop motion anime. Focusing on a scene at a time.