These simple-sounding but powerful principles keep resurfacing in my work, and a quick reminder never hurts.
My current favourite is "aesthetic and minimalist design":
Dialogues should not contain information which is irrelevant or rarely needed. Every extra unit of information in a dialogue competes with the relevant units of information and diminishes their relative visibility.
I keep running into the proponents of "what’s the harm in a little more info?", and I find this principle of "relative visibility" compelling. I’ll see how well this works as an argument for not overloading the user with "just in case" information.