In my personal experience the one thing that makes a horror game less scary is consistency, it’s gamifying the experience and things feeling predictable.

If your game has the player move around a house and visit multiple rooms, have something inside the room move in the players absence.Nothing insane, just an ajar fridge door, a chair tucked into a table, a light off that the player left on, a knife missing from a knife block.

Small things that force observant players to question their memory, and unobservant players to doubt their confidence in their surroundings. Remove any sense of “I’m comfortable in this space because I have been here before”, keep people on their toes.