You could make everything dark with tint and stuff.
Add cobwebs to make it look like its been abandoned for a while.
Add patches of dead grass.
Also adding big shadows covering the world makes it look scary I guess.
watch a plot summary of some edgar allen poe to get some ideas for what makes things scary. maybe internal dialogue, things disappearing and randomly reappearing, strange coincidences.
in short, dont make the story scary on the outside, make it unsettling.