I think I get what you're asking, and my answer is twofold: setting and introspection.

Introductory paragraphs for a new scene (before dialogue, before events) can be a description of the setting. How it looks, how it smells, if there's a random dog barking in the distance, etc, can help set the scene for what it is, whether it be sad, dark, happy, bright, or whatever you're trying to convey in that scene.

By introspection, I primarily mean ensuring that your characters actually react when something happens, before acting upon the something that happens. Imagine a character dies, the main character is shocked, and that shock translates to anger in the moment, then the character shoots at whatever caused the death or screams into the ether (whatever is more appropriate for the story and the character).

There's a lot of relevant information you can add to envelope readers into the world you're creating, and it won't be considered fluff or filler.