The first one: I woke up in the middle of the night to a noise downstairs. When I looked down from the top of the stairs, I saw my own face staring back at me. Another one: She heard a knock on the door. When she opened it, there was nothing but a cold handprint on the doorknob.
I was alone in the school gym. A cold hand touched my shoulder, but when I turned, there was no one there.
Another really scary one could be 'My phone rang at 3 am. The caller ID said it was me.' It plays on the idea of the self being something other or unknown, and calls at that time are always spooky.
I saw a figure at the end of the hall. As I blinked, it vanished, leaving only a chill.
She heard a knock on the door. When she opened it, no one was there but she felt a cold hand on her shoulder.
She opened the old wardrobe. A pair of eyes stared back at her from the darkness.
I woke up to a cold hand on my shoulder. When I turned, there was no one there.
I woke up to find a handprint on my window. It was on the inside.
I think 'The clock stopped at midnight. Then I heard footsteps.' is quite scary. It gives this feeling of something ominous starting right at a spooky time.
I think 'I heard a child crying in the basement. But I live alone.' is quite terrifying. The idea of a crying child in a place where no child should be, especially when you live alone, plays on our fears of the unknown and the supernatural. It makes you wonder what could be down there, and the thought that it's not a normal, explainable situation is very frightening.
A third story could be: 'I took a photo of the cemetery. When I looked at it later, there was a figure standing behind me that I didn't see when I took the picture.' It gives a feeling of unease as it implies that there was some sort of ghostly or otherworldly figure present at the cemetery that the person was unaware of until they saw the photo.