I believe real connections are made between two people only when each presents herself to the other party as she really is.
We've all been waited on by someone who clearly is playing a role; it often feels awkward (it might not be the person's fault, I get that). Unless one is a very skilled actor (most of us aren't), one can't make it click with another human if one presents one's "professional me" face that's vastly different from who "real me" is.
Be nice. To everyone.
In the sales game, it happens that someone walks past the people deemed "unimportant," not saying hi, and goes straight to see the perceived alpha (buyer). First, the reasoning behind being nice selectively just sucks. Everyone is important because everyone is a person. Also, acting like this will bite you back in the ass. The barback/cashier person might become the next decision-maker here or somewhere else. She will remember one and one will have deserved it.
Ego is the enemy. Turn it off. Be humble.
One is neither better nor smarter nor more important. Nobody cares about one mentioning one’s own accomplishments. The way these might matter is if one keeps one’s head down, and as they pile on, people take notice without one mentioning anything. Ego is what makes one dismiss someone's ideas or opinions. It's what makes one not listen to an answer while just thinking about what one has to say. Not helpful.
One has little to no idea what some of one’s colleagues, friends, or people one interacts with on the daily are going through in their lives. Have patience.
One might have a smile during the day only to come home, over and over again, to a dramatic situation. Don't assume people's default mode is that all is well. Those who have gone through really rough times, or still are, know (be strong). Those who have not encountered true chaos should give others the benefit of the doubt: this snappy reaction, comment, or action might have deeper roots than the obvious.