Once you've got your dialogue punctuated and formatted correctly, it's time to focus on the style and character.
USE ACTION BEATS Action beats are a smooth way to attribute dialogue to the speaker without using tags. When you write an action directly before or after a line of dialogue, the reader understands that the dialogue belongs to the active character. Action beats help the dialogue to flow.
Sarah haltered the gray gelding and brought him over to the tie post. “This is your horse. His name is Lucky.” Grammy picked her way around a puddle and ran a brush across Lucky’s crusty coat. “Oh he’s white just like Cotton, the horse I rode when I was young.”
AVOID ADVERBS Using adverbs to describe how dialogue is spoken is considered amateurish, and is a lazy way of adding tone to dialogue. Good dialogue conveys tone and emotion in the words themselves. Let your words do the work and use an action beat to show instead of tell.
Before: “You’re going to put me on a horse?” said Grammy nervously.
After: “You’re going to put me on a horse?” Grammy wiped her palms on her blue jeans and took a deep breath.
GRAMMAR CAN GO It’s acceptable to write grammatically incorrect dialogue with poor word choice if that’s how the character would speak it. If a character speaks in broken English or in dialect, write it. But keep in mind that too much of this type of dialogue can fatigue the reader.
Read your dialogue aloud. People don’t speak the way they write. Reading dialogue aloud will show where it sounds unnatural, stilted, or too formal. You have permission to write fragmented, ungrammatical sentences.
Formal (unless you're writing Jane Austen fan fiction): “Would you accompany me on a horseback ride? Natural: “I’m going for a ride. Wanna come?”
WRITE WITH PURPOSE Make sure your dialogue moves the story forward. Dialogue should serve a purpose, avoiding the dull and obvious. Avoid small talk and pleasantries unless they contribute to the story.
KEEP TRUE TO CHARACTER Each character should have a distinct voice. Is this something this character would say? The brash rebel isn’t going to politely ask someone to move out of the way. The innocent little girl isn’t going to say something with innuendo. The scientist may drop a scientific term in or the professor may speak eloquently. Dialogue should match the character’s level of education, career, personality, etc. Dialogue should also vary depending on who the character is talking to. The police officer is going to talk differently to his mother than he would to a co-worker.