https://www.ohio.edu/nor/a/content/pdfs/Makkai.pdf
First, read Rebecca Makkai’s craft essay “That Dialogue Assignment” (PDF attached).
THEN:
1) Write a dialogue, between two characters, of at least a page and a half. Use the character from Fiction Exercise #1, or choose from the list below:
A dishwasher in a fancy restaurant
Someone throwing a surprise party
A little girl watching a magic trick
A high school student in a pick-up truck
Someone camping with their child
2) Write the dialogue again, from scratch, but make it half as long. Cut down to what’s essential, to the lines that reveal character and create story. Get rid of basic small talk, dead-end banter, people asking each other to pass the salt.
3) Write the dialogue again, from scratch. This time make it six lines of dialogue