Of the three cornerstones of storytelling, characters have to put up with a lot. Not only do they have to respond and react to the movements of plot, but they do so within the constrains of their setting. Their motives are constantly questioned and everyone almost always wants to know what their goal is.
It’s no wonder your characters should and do feel a lot of things. From joy to disgust to rage and even hopelessness, your characters have an entire gamut of possible emotions. As a writer, your job is to help portray those emotions. Body language absolutely should be something you familiarize yourself with, and so should the array of human emotion.
For that, I recommend an emotion wheel.
You might also see this referred to as the wheel of feelings. In essence, it breaks every emotion down into its basic elements—Embarrassment is rooted in hurt, which has roots in anger. Confidence takes a base in pride, which in turn stems from happiness..
Essentially this functions as an extended thesaurus, not only giving you an accurate word for what your character is feeling, but giving you an idea of why they might be feeling that way, and how they might express it. Both disgust and boredom can be conveyed by having a character support their head on one hand, either with a sneer in place (disgust) or a blank expression (bored).
Keep in mind that emotions are fluid and aren’t necessarily bound to follow a logical order. Not only does sadness turn into fear, it can also turn into disgust or even hope. Just as easily, happiness can turn into anger.
As an exercise: Go to any stock photo site such as pixabay or unsplash and search for a base emotion—anger, fear, sadness, happiness, disgust or surprise. Pick out three different images and analyze them. What are some of the similarities in the models’ body languages? What are some differences? What higher-level emotions might each model be feeling? Write down those cues and clues as a reference the next time you have a character feeling a particular emotion.