Show, don’t tell. It’s the number one rule for a writer. In that spirit, here are two paragraphs. Which one pulls you in more?
Jimmy was nervous. The detective had badgered him for hours, and he wasn’t sure how much longer he could dodge the questions.
telling you how Jimmy feels
or
Jimmy’s leg shook under the table. This detective kept asking him the same questions. Jimmy scratched his head and glanced from the door to the clock. “Didn’t I answer that two hours ago?” he asked. Where was his damned lawyer?
showing you Jimmy’s anxiety
When you tell the reader a thing, the entire burden of picturing that is on the reader. It gets the point across, but is pretty dry.
When you show the reader what’s happening, they can infer the thing you wanted to tell, and have a much richer idea of how it manifests. This is, after all, how it works in reality. We can’t see into each other’s minds to know for sure how we feel. We infer it from observable behaviour.
This is where the Emotion Thesaurus becomes very useful. If I’m writing a scene and know how a character should feel but can’t immediately picture their actions, I can open the Emotion Thesaurus to the relevant section and get a variety of visual cues for that emotion.
Each section matches a feeling on an emotion colour wheel. This has the added benefit of capturing the depth of emotions. For example, both guilty and remorseful fall under the category of sad but are different degrees of that feeling. As such, how a character might exhibit that feeling also changes.
It can become a crutch though! It becomes very easy to just reach for that thesaurus any time you need to express emotion, and then go down the list till you find an action that suits. I caught myself doing that while editing a recent draft, and had to resist the temptation.
Since you already picture your characters as people having emotions, think about how those emotions surface. Little twitches to massive outpouring, whatever is appropriate. You know best how your characters behave. Often just looking at the colour wheel helped me define the exact feeling, then made it easier to know what the character would say or do. For those times when you’re stuck though, the emotion thesaurus is the perfect tool to give you ideas on how to show rather than tell those feelings.