My first piece of advice when writing horror and creating tense scenes: Read it!
Referencing a book or short story that had you on the edge of your seat – that's the best place to see exactly how other author's created tension and suspense. Now, how can you weave that same suspension into your own writing?
1.) Don't tell the reader everything. Imply.
Instead of writing, 'Jody heard the doorknob turn.' write -
'Jody heard one dog bark, then a second. Why wasn't Spike barking? Spike always barked when the neighbor dogs did.'
Do you see the difference? In the first example the reader knows somebody is trying to get in the house. It's direct and to the point. The second example creates an element of fear – why isn't her dog
Spike barking? Who out there is preventing this?
2.) Let your character tell the reader their plans
Nothing is scarier than having a character announce his or her plans. As readers we cringe...why did they have to say that out loud? They should have just thought it and then did it.
In horror, announcing plans out loud is tension gold. If you're reading this right now then you might be a horror fan and know, without fail, that announcements are the precursor for disaster. And there's nothing juicier than knowing your character has just set themselves up for something disastrous. It builds tension.
Instead of writing, 'Jody thought about throwing the doll out.' write -
“Alyssa, you guys were right, there's something very wrong with that doll. Somethings been really off all evening. I'm going to throw her in the garbage as soon as I get off the phone with you.”
“Make sure she goes outside, Jody!”
“I will. They pick it up tomorrow so she'll be gone for good.”
It might be hard to feel the tension in that last dialogue as I've included no back story (I will at the end), but my point is the announcement. Especially that, 'she'll be gone for good' part. By allowing the character to announce his or her plans escalates the feeling of tension the reader feels. Using this example, the reader knows Jody will have to touch the doll to throw her away – how will that exchange go? “She'll be gone for good”...really? Jody just told us there was something very wrong with the doll and things have 'off' all night. How exactly will Jody get rid of this doll 'for good'?
Creating tension also makes the reader want to read more!
3.) Connect your reader with the character
There are many things most of us are afraid of: spiders, snakes, being in a dark house alone, a shadowy alley in a shady neighborhood, a stranger in the house. In writing horror you want you reader to immediately feel the tenseness your character is feeling.
Instead of writing, 'Somebody had cut the electricity and Jody's eyes could not adjust to the dark. She listened to her own breathing until she heard someone's else breathing join hers.' write -
'Somebody had cut the electricity and Jody's eyes could not adjust to the dark. She heard them, then, stealthily join her in the room. Her had shaking she reached for the flashlight. Now she would expose whoever this was. Sliding the button forward she waited for the light, which never came. The battery was dead. And the breathing came closer.'
Notice how the defunct flashlight amped up the unsettling feeling of being alone in a dark house with absolutely no light? How did you personally feel when you read that paragraph? I know at this point in the story I'd be yelling at Jody to get the hell out of the house!
Always remember, one of the necessary, driving factors for feeling suspense or tension in a story is reader empathy. If you haven't created a character your reading audience cares about they won't care about his or her demise.
Back story: Jody (earlier in the day) had purchased a large, creepy looking Victorian doll at a flea market. Her friends all insisted she not buy the doll but, of course, she did anyway. So she gets home and weird things start happening (which she aptly attributes to the doll) and throws it in the garbage. So now its outside (thus Spike might have been mangled by this doll) and now she's alone in the house with it – the lights out.
The fun thing about horror writing is you don't have to stick to non-fiction situations. Killer dolls are perfectly acceptable.
And if you make your readers think twice about buying a doll at a flea market, you've done your job as a writer.