I believe that in order to write horror, you need to have been very, very afraid at some point in your life. It helps to have a lot of fears, like Poe, so that you can use them when you need them.
So I think that if you're thinking of writing horror and you've never had any great fear, a good idea would be to spend a couple of nights, alone, in the woods. It would help if you can go so far out that you can hear no trace of humans. No cars or talking.
Only use your flashlight for emergencies and bring candles.
When night falls, turn off your flashlight, stay in your tent and just listen to the sounds of the forest. You'll be terrified. Animals you can't identify will come sniffing around, there's nowhere to go. When three in the morning comes around and you find you have to go to the bathroom, you'll find out how courageous you really are, especially if you're not going to use your flashlight.
After all that, after you've reached down into your greatest fears, you'll be able to use them. But you do need to feel them first.