These are basic tips for writing dialogue that I've learned over the years from workshops with major Canadian writers.
Dialogue for scripts and stories requires different approaches. With a script, the actor's tone will deliver the message. With a story, the reader must understand the message. My two recent phone-calls will illustrate the differences.
People phoned me on the same day asking for charitable donations. I'd run out of money, so when the first person, from MADD, asked for $25, I said, "Sorry, I can't help you." He said, "Yes, right" and hung up. To the second man, from the Police Association, I said the same thing, "Sorry, I can't help you," and he said, "Yeah, right." Almost identical replies, but the tone made the difference between courtesy and rudeness.
If I'd been reading the replies on a page, I might have missed the difference. Professional writers tell you not to tack on an explanation. Avoid "Yeah, right," the man said rudely or "Yeah, right," the man said sarcastically. These days, workshop leaders also tell you not to hype up your verbs. It's "he said," or "said he," NOT "he snarled" or "he sneered."
If you think the reader of your story will not understand the tone of the words, change them. For example, have the Police Association guy say: "You've got to be kidding." Or "You just don't get it, do you?" Or give the other speaker some inner thoughts. For example, "When he said, 'Yeah, right,' she could hear the sarcasm in his voice."
Or give the second speaker some dialogue.
"Yeah, right," he said.
"You're a nasty bastard," she said.
— Ann Birch, author of The Secret Life of Roberta Greaves (fall 2016)