Punctuate dialogue correctly and write an exchange that reveals character through word choice rather than through dialogue tags.
Dialogue has two jobs at once: it has to sound like real speech, and it has to reveal something -- character, conflict, or information -- that the story needs. The mechanics are non-negotiable: start a new paragraph every time the speaker changes, and keep commas and periods inside the closing quotation marks ("I know," she said. NOT "I know", she said.). Getting this wrong is one of the fastest ways a piece of writing loses credibility with a reader.
Weak dialogue leans on adverbs to do the emotional work the words themselves should be doing: "'I'm fine,' she said angrily." Strong dialogue lets word choice and rhythm carry the feeling, so the tag can often just be "said" or vanish entirely: "'I'm fine.' She didn't look up." The second version trusts the reader -- and it trusts the words enough not to need the adverb crutch.
Mastery looks like: They can correctly punctuate a multi-speaker exchange and write dialogue that reveals emotion or character through word choice rather than adverbs or dialogue tags.
Common stumbles: Running multiple speakers together in one paragraph; defaulting to adverb-loaded tags instead of trusting the dialogue itself.
See it visually
Interactive, spoken-aloud tools that show this idea in motion.