This is what they call in the swordsmanship schools “a secret technique.” Only I’m talking about writing, not swordsmanship.
Where do you find great dialogue?
From real life.
Yesterday, at the Chinese restaurant, I paid for my order and, as I was leaving, said to the cashier, “Ta-ta.”
“Ta-ta? What’s that?” he asked.
“It means bye-bye,” I said; and drawing on my meager stock of Chinese, added, “Tsai-chien.”
Whereupon he smiled and replied, “Adios!”
Or this one, from a day at the ballpark: a woman called to the vendor, “I’ll have a hot dog–with the works!”
He answered, with a show of great patience, “Lady, this is Yankee Stadium. You get a hot dog, a roll, and a little mustard. That’s the works.”
Keep your ears peeled for the way real people really talk. They’ll often surprise you with nice bits you can use in your writing.