Good dialogue sounds like real speech when you read it, but is is not real speech; it merely sounds like it when read from the printed page.
Good dialogue serves any of several purposes. It conveys information, advances the plot, makes complicated developments understandable, or deﬁnes and reveals your characters. Good dialogue is a form of slight-of-hand because it isn't real, but it seems to be real. With good dialogue you lead readers to think the characters are speaking as they do in everyday life, when - in fact - they're doing nothing of the sort. What people speak in normal life is conversation, not dialogue.
As my late friend and mentor Gary Provost used to say, “Dialogue is conversation's greatest hits.”
Witness this exchange between two bad guys in Elmore Leonard’s novel, Killshot:
“I popped him one time.” Armand took his hand from the steering wheel and pointed to his mouth. “Right here. One shot.”
“One shot, one kill,” Richie said. “What'd the guy do?”
“I mean what'd he do you had to blow him away?”
“I don't know. I didn’t ask."
“It’s not any of my business, it was a job.”
“You blow a guy away, it’s none of your business?”
“Whatever he did isn’t, no.”
“Were you pissed off at him?”
“I didn't know him. Don't you understand nothing?”
“To me that doesn't make sense," Richie said. “Me, I have to be pissed of at the guy.”
That’s great dialogue. You can almost hear the rhythm, and it also did a lot of work in deﬁning the character of those two guys. Although both are killers, Armand kills without remorse and Richie has to be “pissed off at the guy.” They revealed themselves in their own words.
One thing Elmore Leonard did which I think is really wonderful is to leave words out of his dialogue. “You sitting down?” instead of “Are you sitting down?” He comes close to the way people really talk and still accomplishes what good dialogue must accomplish.
Dialogue also needs to be there for a purpose. Pretty writing alone is useless if it doesn't perform a storytelling function. Giving dialogue a purpose means that every line of conversation in your novel must earn its place.
Dialogue should characterize, give information, or advance the action of the plot in some way.
Avoid dialogue that does not have a purpose:
“Good Evening, Sir. My name is Carla. May l get you a drink?”
“Yes, please. I would like a martini with two olives.”
“Sure thing, sir. I'll be right back with your order.”
That kind of dialogue tells readers nothing.
“Why, Frank, l haven’t seen you since high school, right after your parents were killed in that air crash in San Diego, when a navy jet flew into that 747 and 250 people died, and you had to go to work selling vacuum cleaners and missed going to medical school.”
The speaker is telling Frank stuff he already knows. Information overload (aka infobesity or infoxication) refers to the difficulty a reader can have understanding an issue caused by the presence of too much information.
Many writers pack so many facts into dialogue that conversation, which should be natural sounds artiﬁcial and mechanical.
But, don’t misunderstand: The primary function of dialogue is to inform while blending character and action. Just don't overdo it.
Above from the book NOVEL SECRETS,
available for Kindle for only $.99 cents: