Showing instead of telling means showing the consequences of a character state (anger, anxiety, love, worry, hate, etc.) instead of labeling the state.
"Steam coming out of her ears" is a cliché, originally intended as the consequences of a metaphor for the heat of anger, itself not necessarily literal, but a reference to flushed skin causing a redder appearance.
What do people that are nervous do? They may shake, stumble over words, be clumsy, and spill something. They are often anxious about the outcome of what they are doing, like blowing a job interview. They may make inappropriate comments or jokes, trying to be funny and alleviate the tension that only they really feel. The tension and worry they DO feel may be distracting and cause them to make mental mistakes: Call their interviewer by the wrong name, for example, or blank on a rehearsed reply to an interview question.
Or, if they are making a presentation, get flummoxed by an unfamiliar projector or piece of computer equipment, or a clicker for the slide projector that doesn't seem to work as they expected, or speaking too closely into a microphone and startling themselves with the result. They may blush at their mistakes. They may sweat.
There are many possible consequences to being nervous, pick a few, and use them. Or use the general idea (distraction and worry) and come up with an original ramification for it: a consequence, an implication. Describe something visible or tangible.