I'm repurposing this post that I wrote over at YAKnow because I think it's important to note!
As writers we are constantly told to make our details concrete, to avoid cliches, and to engage the reader and ground them in the story. Most of us love to be creative - and can go quite in depth, describing a red and white striped room as a glorified peppermint candy. Or we get sensory with a dense cherry cupcake oozing a jelly filling.
But, while you - the writer - may want to showcase specific details, it's really all about your character. When it comes to descriptions - you need to get inside your character's head. That means taking note of her interests, her background, her desires, and the emotions and actions of a particular scene.
For instance, a teen probably wouldn't take note of the walls in a room - unless they were extraordinarily obnoxious or triggered some sort of significant memory. And he wouldn't notice the density filling in a cupcake - he'd probably devour it in two bites and ask for another.
So what do they pay attention to? If your character is into art - she's going to notice color, natural frames, textures, and of course any artwork in a room. If he's a comic book fan, he'll describe his friends and setting associated with those of his favorite characters and cities. And, of course, the action of your scene dictates what your character has time to notice at all. When they are immersed in a fire they won't take time to note the bright orange flames licking at the grandfather clock in the corner.
Nope ... they'll be running for their lives.