I've studied a lot of books about methods to improve my writing. I've seen some good advice, and I've seen some bad. A bit of good advice I recently heard was studying the storytelling methodology of popular books and films. It isn't a new concept, but this book called A Damn Fine Story used a lot of popular film and story examples to demonstrate how you go about that. I recommend the book, and I'd also like to share a little storytelling methodology I recently spotted while rewatching a favorite comedy sitcom called My Name is Earl.
Maybe you are familiar with the show. It focuses on Earl, a local criminal who turns over a new leaf to improve his Karma. I noticed from Earl that a notion of unforeseen consequences attached to his bad decisions. In every episode, he starts trying to fix what looks like a straightforward solution, only to learn that his crimes have more depth than he anticipated. Tricking a golfer into believing he hit a few hole-in-one shots to get free beer convinced the man he should be a PGA superstar. He ended up losing his job, girlfriend, and dog. Earl finds out he has to do much more than buy the man a bunch of beer to correct his mistake.
If you're wondering what this has to do with fantasy writing, this concept can give all writing fantasy or not more depth. When you think about all the characters affected by a protagonist's decision, those decisions can have a domino effect throughout the story. Even a minor detail can do significant things.