How To Write Horror????

I've recently started getting interested in writing a horror story. It won't be long, as I prefer writing short stories. The problem however I've faced is that I've never written horror before. I've no idea how to make it scary and whenever I start I give up because it doesn't feel scary. Does anyone have any tips to how to write a horror story or something they enjoy when they read them?

The idea is that the story surrounds to people, a man and a woman. The man has invited the woman home and she's planning to eat him. Also important to the story is spiders, which is something I personally think I'll be able to use for the benefit of the scary. 

All tips and tricks is welcome!