To begin with, his use of adjectives allow the reader to visualize the characters and setting. This makes the reader feel like he is in the story and watching what is going happening.
Next, He gives the reader clues. These clues allow the reader to understand what is going to happen. One clue that got my attention was when Billy looked through the window, I knew something was going to happen when I read that. And, when the Landlady invited Billy to come into her house, that gave me a clue that something was wrong, and very creepy.