One more for you. 'She walked into the empty basement. A strange whisper told her she would never leave.' The basement is often a place associated with the unknown and danger in horror stories. The sudden whisper indicating that she's trapped is very scary.
A good one is 'The doll's eyes followed me. Then it smiled.' Dolls can be really creepy, and the thought of its eyes following and then it smiling is quite unnerving.
The moon was a pale, sickly orb, casting long, distorted shadows that seemed to writhe like living things. The wind howled through the bare branches of the ancient trees, sounding like the wails of the damned.
Make the sentences vivid. Don't just say 'It was scary.' Instead, say something like 'The walls seemed to ooze a dark liquid that smelled of decay, and the air was filled with a deathly silence.' Vivid descriptions make the horror more palpable to the reader.
The brevity. With just two sentences, they create a sense of mystery and unease. There's not enough space to fully explain what's going on, leaving a lot to the imagination.