One way to distinguish a culture is their greetings and farewells, but what all cultures have in common is the willingness to do them because it’s a hallmark of goodwill, respect and civility. We can surmise that in a truly barbaric society (one that also has little culture), these greetings don’t exist or are not much more than eye contact and/or a grunt, but most societies that world builders need to invent have more than this.
Greetings are typically more involved than farewells because they set the tone for the coming interaction, but when there’s to be no real interaction (such as passing someone on the street), they’re short. An acknowledgement is among the most basic of expectations, and yet some situations do not call for them and not everyone will comply even when they do (just as some will do them when not required). In a big city, people walk past each other on the street with no acknowledgement and it might even be considered weird for us to say hello to anyone.
As world builders, we should aim for brevity because the audience doesn’t really care about these moments unless something goes wrong during them. Why waste a paragraph or five minutes of screen time? It’s similar to an issue in Game of Thrones, where Daenarys had so many titles by the end that it took thirty seconds to rattle them off, and the show repeated this in every introduction instead of bypassing them. Never make the audience want to skip ahead.
Many potential failures exist in both greetings and farewells; storytellers can leverage all of them for tension. Some people will not respond to one at all; we don’t need to first establish that a response is expected because our audience will assume so (it’s implied), especially when other characters react to this. The unresponsive person likely knows they’re failing in this, unless they didn’t hear/see it or are distracted. Reasons for this are a storytelling issue, as culture doesn’t explain a total lack of response or acknowledgment when doing so is universal across cultures.
By contrast, culture can explain responses that are considered inadequate, a fact that may surprise the one giving the inadequate response. It’s almost a given that, without previous experience in another culture or someone telling us what to do, we will make mistakes. The degree of these will depend in part on how different the two cultures are (the one we’re in and the one we’re from). Ignorance is not the only reason for giving offense. Shyness can cause it, as can previous bad experiences that leave some fearing more of the same and performing poorly. Some people use too much or too little strength in gestures, such as a meek or crushing handshake. People are always interpreting the actions of others and some cultures might be more prone to finding offense.
We may want both formal and informal greetings in our setting. In English, “hello” is more formal than “hi,” which is not as casual as “hey,” which still stands above “yo.” Then there’s “What’s up?” or its shortened “’sup?” We don’t need so many as this, and there are plenty more in America, but it’s realistic that our traveling characters will greet comrades one way, strangers another, and those of a different station a third. Consider creating these variations.
Greetings sometimes have a practical origin, such as the handshake being designed to show that neither person has a weapon, or even to dislodge a dagger hidden up one’s sleeve. A variation on this is to grab the upper arm. With alternate weapons in SF, we might think of a different greeting that has a similar purpose. Think of how a sneaky person would conceal an item and what gesture might reveal it and become commonplace.
In addition to greetings, some of what follows can also be done to congratulate others, thank them, say farewell, or confirm an agreement.