Timing is very important. Suspense is a must but when I read Stephen King's "Pet Sematary." (Misspelling is part of the title.) I grew impatient and thought with all my might "JUST DO SOMETHING ALREADY!"
Now, inspiration is the tricky bit, but think about this: People aren't of the dark, they're afraid of might be in the dark...That is, the unknown. Don't actually show the monster, let the audience turn it into what they fear most.