Quiet leaders don’t announce the standard. They just keep meeting it until everyone else catches up.

Describing a standard makes it an opinion; meeting it over and over makes it the weather of a group. People adjust to what they see happening around them much faster than to what they are told, especially when whoever is telling them is inconsistent about it. The slow version works because it never gives anyone anything to argue with.

Choose one visible behaviour you want to be normal, then do it every single time without commenting on it. Expect several weeks in which nothing appears to change. Say something only if somebody asks you why.