With my entry I tried to create a horror experience by taking an environment and situation that is relatable. In my case its a bedroom and the relatable aspect is being afraid of the dark, which many of us experienced as children and some still do to an extent as adults.
I also made an effort to have the game go slowly and build tension through anticipation. The game also signals that the ghosts are there without immediately showing themselves. You'll hear them or the indicators on screen will identify that there is activity taking place and then its up to the player whether they want to look now or later. They know they will have to look sooner or later to progress, but they have to decide if now is the right time or not.
I think these are what worked for my game anyway.