There is very little in fiction that is utterly new. Everything stands on the shoulders of that which came before it – the prior art. And that’s fine. There are an infinite number of ways to mix together existing ideas, styles, characters and themes, and to throw in a few new ideas as well.
You have to keep the prior art in mind, though, because the reader will have all these existing cultural references bubbling away in their subconscious when they get to your book. For example, I can’t pick up a vampire book without mentally cross-referencing it against Stoker, Rice, Whedon and Meyer. (Vampires are a particularly good example, because there are so many variations of the ‘rules’.)
Prior art can be useful to a writer because it creates a shorthand. You don’t have to describe the rules for your chosen paranormal creature, because most people already have an idea of them. All you have to do is describe the deltas, the deviations from the established rules. It also gives the potential for dramatic irony, because the reader can use his or her knowledge to figure out what’s coming before the characters in the books do. (Of course this can be irritating. Characters in books can seem particularly dense if they fail to catch on, yet we know that they are in possession of the same pop culture and prior art knowledge as the reader.)
The downside of prior art is that the first or most popular example often overshadows others. It creates canon and sets rules that are then hard to break.
Here’s the prior art pickle that I find myself in. I’m writing a series of books about faeries set in Yorkshire. For the second book I wanted the main villain to be a local aquatic faerie that pulls people into the river to drown them. Yorkshire/Northern water faerie that likes to drown people? Got one of those. Job’s a good un. Or is it?
If I say the word ‘grindylow’ to you, what do you immediately think of? The pesky little creatures in the Harry Potter books that can be dismissed with a single blast from a wand.
That association doesn’t work well for what I want to use this creature for. My villains need to interact with the main characters on an even footing. They need to be much more threatening and anthropomorphised. Two choices. 1) Pick a different faerie villain. 2) Take the hit. I went for option 2.
My current draft deals with the disconnect between my story and JK Rowling’s prior art by hanging a lampshade on it early and then getting on with the story. Anything else would be disingenuous. My novel is set in the present day UK, there’s no way most of my human characters would not have read Harry Potter.