Show, don't tell
Show through action, gesture and detail rather than assert through adjectives: "he clenched his fists" rather than "he was furious."
"Show, don't tell": prefer scene, gesture and sensory detail to abstract assertion. "He was generous" reads and fades; watching him slip his gloves to a freezing stranger stays. The shown version engages readers, who deduce for themselves — and we always believe what we deduced more than what we were told.
The rule isn't absolute, though: telling is the legitimate tool of compression (three months in one sentence), transitions, and information without emotional stakes. Showing everything would make a novel endless. The useful split: show what must be *felt*; tell what must be *known*.
Example
Telling: "she was afraid." Showing: "she checked the lock twice, then dragged the dresser in front of the door."