The person mopping the hall deserves the same “good morning” as the principal.

How you treat people who cannot affect your standing is the most accurate measure available, because nothing is being bought with it. Courtesy aimed upward is ordinary and easily explained by self-interest. Courtesy that runs in every direction is simply how you operate. People clock the difference immediately, including the people being skipped.

Greet everyone in a building the same way for a week, staff included, with no exceptions. Learn one name you do not currently know. Notice how different that building feels to walk through afterward.