Research your story inspirations:
Even fiction has to be at least somewhat believable
Covered some of this in the bit about reading, but this is important and usually a pretty fun part of the creation and planning process. Well, for me it is but I enjoy research and studying, probably on a whole different level than others. Researching inspirations and events, culture, beliefs, etc. that you want to use in the story is a very different experience than just trying to pull it out of your butt and hope it works out. I enjoy using mythology in my stories, because learning about mythology is a great way to learn about different cultures and why the belief structure is the way it is It’s also awesome to see the difference and similarities in cultures that I might not otherwise notice. For instance, I decided a year ago that I wanted to write a story about Djinn in a pre-Islamic context. You wouldn’t believe the time I had finding research materials on Djinn and mythology for the time-period.
However, the payoff exceeded what I hoped for because I’m learning about a culture of mythology I haven’t previously studied and it filled in some of those holes for insight into my own writing. Another important piece is research on something you want to write about, even you made it up, makes it more believable and thus relatable if its existence grounded in something known in this realm. You can use castles, vampires, and dragons in a fantasy story because pretty everyone has seen or at least heard of one, but change the word “dragon” to “wyvern” and you may have fewer people that know what that is. It’s a type of dragon but, more a specific species and that makes it interesting. Use the name of a specific type of fairy folk or the term Oberon’s children or even the name or history of an existing castle, and you get a different reaction than just using the term for it because there is culture and history behind the specifics that the general term just doesn’t have. It has a connection that allows for more interesting information to be staged about a place or character, than just making its background material.