Right now, I'm reading Writing Horror edited by Mort Castle (I think it's an older edition of a book I already own) and I've recently returned to the library the newest edition of F. Paul Wilson's Nightworld. That's gotten me thinking about ways to improve my own writing, particular the horror or more horror-oriented parts of it.
Two important pieces of figurative language are simile and metaphor. One of the essays in Writing Horror points out how useful creepy similes and metaphors can be in setting up an atmosphere of dread.
Here's a selection from Nightworld. Evil millennia-old sorcerer Rasalom has implanted himself in the ground beneath Central Park and is undergoing a physical transformation fueled by the fear, pain, etc. of the world he has caused to fall progressively into endless night (with swarms of nasty bugs and other creatures to make things more fun).
And as he feeds, Rasalom gains mass, grows larger, thicker. The granite walls of the pocket flake away to accommodate his increasing size. The chips slide to the bottom and collect there like shattered bones. (pg. 96, Nightworld, F. Paul Wilson, 2012)
As if things weren't unpleasant enough, "like shattered bones" provides more dark imagery.
I've put this to work in The Thing In The Woods. I've written some short horror stories and published them either independently ("Melon Heads" and "The Beast of the Bosporus") or sold them to others ("I am the Wendigo," "Nicor"). Thing will be my first horror novel and given my mixed success writing horror, I'll need to up my game.
Although only the prologue has been completed, I was sure to include some dark figurative language. For example, the wind blows over the bare skin of a sacrifice victim like a knife scraping over bare skin. I think I have some more of that--and if I don't, I'll need to add some. The prologue features a human sacrifice and the first appearance of the titular thing and then we don't see overt supernatural doings for three or so chapters, so it'll need to be awesome.