I'm writing a psychological horror story and want to make it truly unsettling. What are your tips for creating psychological horror?
Videos
You can have a narrator who is completely reliable, as in everything you see from their perspective is true and happens exactly as they represent it, but who lacks important knowledge and so presents a skewed picture of the situation. This allows you to tell the truth and nothing but the truth while not telling the reader the whole truth. Preston & Child's Special Agent Pendergast series does this very effectively, they use multiple POV characters all of whom freely and accurately share what they know about the situation, (although sometimes Agent Pendergast leaves the audience and other characters out of the loop about some things he suspects but isn't sure about until after he's been proved right or wrong), without ever giving the audience the full picture until the very end of the tale, and even then there's usually some loose ends. Mysteries/thrillers are not my usual fare, I don't like feeling lied to and I'm too well read to trick otherwise, but I rather like this style of presentation, and even skipping to the end of the narrative doesn't actually tell the reader how it all went down.
I don't know that you need an unreliable narrator to write psychological horror.
An unreliable narrator is one whose observations we cannot trust, usually because the narrator is lying or because the narrator is mistaken.
Psychological horror are stories that play on the audience's fears by presenting situations that are frightening to most people: being deceived by the people we trust, fear of the dark etc.
Psychological horror often does use unreliable narrators, but that is not necessary. What you need is a viewpoint character who experiences a frightening situation. For example, most people (possibly around 70%), are afraid in the dark at least sometimes. This fear is increased if there are unfamiliar sounds or dark figures. So all you need to induce psychological horror in your audience is to send a woman who has just read a news article about an incident of rape in her neighborhood into a forest and encounter a male jogger. That would be objectively frightening to most women. The character can be aware of their irrational fears (after all, most rapes happen at home and are perpetrated by people the women know, so a forest is actually a more safe place than the way home from a party accompanied by a male "friend"), the character can perceive both their surroundings and their emotions objectively (and not lie or be mistaken about any aspect of it), and yet it will be a frightening situation if you describe it that way.
In fact, your characters don't even have to be afraid!
Take the same situation, where a woman walks through the forest at night completely unafraid. You can still evoke a sense of lurking danger and make your audience afraid for your character!
I want to write a story about a adopted child who learns that something is not right with his adoptive family. I have the main story elements down, but I don’t know how to make it a slow burn to the end. (Sorry if I explained it poorly)