What key elements do you wish more horror novels had?

I am a new author currently writing my first book. Which I chose the horror theme. Trying my best to make a great book. As I understand first books aren't always best sellers and usally have more mistakes as authors learn .
I have a few questions for other horror novel author or horror readers: What are things you felt was missed or over explained and wished a author would have spent more time on before publishing?

What I plan to include are: Historical element: My story will have elements based on elements of historical events in my story's location. Choosing to not include actual location names.

First two scenes want to jump into a flashback that is explained more later in the book.

My protagonist works though her own trauma. During that time she meets a platonic friend who helps her through her struggles and, as the reader finds out later, has a connection to her past.

Want to hint things I will explain more in book 2.

Would love to know what you guys think would make a great horror novel.
Will include a Spotify podcast that I find I have learned a lot from down below.