How to show, not tell, in a single sentence
Rebuild this sentence in your own words before you read how I would.
Tom was extremely nervous about the audition.
"Show, don't tell" is the most repeated advice in writing classrooms and the least explained. At the scale of a whole story it can feel abstract. At the scale of one sentence it becomes something a writer can practise: the difference between announcing a feeling and producing it.
The sentence
Tom was extremely nervous about the audition.
A composite — built from a pattern that appears on many students' pages, not quoted from any one of them.
The diagnosis
The sentence tells us the verdict — nervous — and trusts the intensifier to make up for the missing trial. But extremely cannot make a reader feel what nervous only names. Nervousness has a hundred physical signatures and this sentence uses none of them, which means the reader is informed of Tom's state without ever standing inside it. Telling isn't a crime; here, though, the audition is presumably a moment the story turns on, and turning-point moments are exactly where a reader needs to be shown.
Three moves
Move one — ask where the feeling lives in the body. Nerves live somewhere: hands, stomach, breath, voice. Pick the one that belongs to this character. A pianist's nerves live in the hands.
Outside the audition room, Tom pressed his hands flat against his knees to keep them still.
Move two — let an object hold the feeling. Feelings shown through objects outlast feelings shown through bodies, because the object stays in the scene. Give Tom's nerves something to do to the world.
He had folded and refolded the corner of his sheet music until it wouldn't lie flat.
Move three — keep the strongest witness, cut the announcement. With evidence this good, the word nervous becomes not just unnecessary but harmful — it converts an experience back into a label. Delete it and check the feeling survives. It does; it's stronger.
The after
Outside the audition room, Tom folded and refolded the corner of his sheet music until it wouldn't lie flat.
The word nervous appears nowhere, and the sentence is more nervous than the original — the reader has been made to watch the fidgeting rather than told it occurred.
The principle
Evidence over verdict. Show the behaviour and the reader convicts; announce the verdict and the reader shrugs. One honest caveat: telling is the right tool when a feeling is minor and the story needs to move — she was tired, and went to bed needs no choreography. Reserve showing for the moments that matter, which is precisely what makes them feel like they do.