You use large, varying, creepy sounding adjectives, nouns and verbs. "I peered over my shoulder, tiptoeing down the hall, terrified of what could be in the room. If I was any louder, who knew...It could lurch out at me in seconds. My hands shook furiously, the silence was filled by the chattering of my teeth. And then, in the quiet, I heard it." See, using big, creepy verbs works. Hope this helps!