A couple rules of thumb I use for crafting evocative descriptions as a GM:

THREE OF FIVE: Think about your five senses. Try to include three of them in each description. Sight is a gimme and a Taste will rarely apply, so that means picking a couple out of Hearing, Smell, and Touch. Remember that you don’t actually have to touch something in order to intuit what it might feel like if you did.

TWO COOL DETAILS: Try to include two irrelevant-but-cool details. These are details that aren’t necessary for the encounter/room to function, but are still cool. It’s the broken cuckoo clock in the corner; the slightly noxious odor with no identifiable source; the graffiti scrawled on the wall; the bio-luminescent fungus; etc.

THREE-BY-THREE: Delta’s 1-2-(3)-Infinity talks about psychological research demonstrating that repeating something three times takes up the same space in our brains as repeating something infinitely. Thus, once you’ve hit the third item in a sequence, any additional items in that sequence are redundant.

Extrapolating from this, for minor scenes you can describe three things each with a single detail. At that point, you’ve filled up the “infinity queue” in your players’ brains and their imaginations will impulsively fill in the finer details of the scene you’ve evoked. For “epic” descriptions, use the full three-by-three: Describe three different elements with three details each.

Like most rules of thumb, of course, none of these should be treated like straitjackets.