Portrait photography isn't just taking a photo of a person, it's trying to tell a story, whether it be in the emotion or the pose of the person in the image. You can see, for example, in this image here in Africa, little girl is a bit scared. You can also see the little stuffed koala that I give every child when I travel.
You can see the mother comforting her, and you can see the grandmother in the background, hands on hips, because they're meant to be out working. Expression is a major story-telling device when taking a portrait photograph, the other one is pose. Just by crossing an arms, we can make someone look angry, by leaning back we can make them look relaxed. And we can tell a story in multiple ways. Another thing to keep in mind and, looking at the Africa photo again, is that the background is extremely important.
The background, the context, everything is part of the story. We have here multiple things happening to tell the story. We have the expression on the face, we have the positioning of the arms and the posing of the subjects, even though it was completely natural, especially with the grandmother in the background, hands on hips. But the entire environment is part of the story telling process. Remember, as a photographer, we are a story teller. A picture paints a thousand words. It doesn't mean that we can be lazier than a writer, it just means that we need to be a little bit more efficient.