When most writers think of precision in writing, they think of it in terms of correct word choice. While there are plenty of great blog posts and pages about that (titled vs. entitled, imply vs. infer, effect vs. affect), what I'm talking about is precision in word choice when it comes to action and description. Especially in horror novels, using a single, precise word can often do the work of a string of lesser words - it can help set atmosphere, convey emotion and frame of mind, and describe an action, all at the same time. One of my favorites tends to frequent Stephen King's books: the "shamble." Great, chunky, creepy verb - you don't want a demon shambling toward you, cuz that would suck. So much more than if it were merely moving toward you.
And precision is a blade you can wield to hack through all kinds of writerly tasks, from choosing an exact feeling (is your protag shocked? Or dismayed?) and action (is the thing crying or keening?) to description (does he have skinny hips? Or economical flanks?) precisely nailing atmosphere (is the room quiet? Or does it ring with silence?). In horror, the right word can make all the difference. And since tightening the dread for the reader is the only way to invoke true horror, you want to lean on those "right" words as much as possible. When you crystallize that moment of dawning horror as the killing blade is raised, you spill more than blood when it comes whistling back down - you'll spill the moment all over your reader, who can only blink, horrified, at what's happening - and then turn the page for more.
What about you? Do you have any favorite, muscle-y word choices?