Survival horror is neat, though I can't think of many lit examples of it (Stephen King's "The Mist" is good). I suggest to play video games that fall under that genre to get a feel for the tone. Play lots of them - the ones that are scary, and the ones that aren't. Why is a game like Amnesia more frightening than Resident Evil 4/5? Why is the original Silent Hill scarier than Silent Hill: Homecoming? Gore isn't enough to make something terrifying; that sense of isolation and desperation is huge.