Horror Atmosphere Builder

I'm writing a horror story with this premise: [YOUR PREMISE]
The primary fear I want to evoke is: [FEAR TYPE - existential dread/body horror/psychological/supernatural/etc.]

Help me build sustained dread by providing:
- 3 early "wrongness" details that hint something is off before anything overtly scary happens
- How to use the setting itself as a source of unease
- A progression of escalating disturbances (subtle to overt)
- The moment of horrific revelation and how to pace the approach
- Sensory details that trigger primal discomfort
- How to maintain tension in "quiet" scenes
- The lingering unease for the ending (horror should echo after the story ends)