Editors talk a lot about voice, and it’s a tricky thing to get a handle on. For one thing, there is an authorial voice; that is, each particular author has their own writing style that comes through regardless of the setting or topic of each novel. I prefer to think of that as writing style—though there’s got to be a better term for that—and preserve voice for talking about characters and narrators.
If you are writing in deep POV, your narrative should carry the same voice as the POV character. If you are not writing in deep POV, avoid generic narrator voice and give the narrator a distinctive voice of its own. (See The difference between your voice and the character’s voice.)
☐ Each character has a distinct voice suitable to their temperament.
In my Word Weavers critique group, we read our pages aloud to one another — that is, someone else reads your own work back to you. This is a great method not only for uncovering awkward sentence constructions, but it can also reveal a wealth of dialog problems. Having someone else read your dialog to you is the number one way to improve your dialog. Reading it aloud to yourself is a close second.
If all your characters sound alike, then there’s a high probability they all sound like you, and that’s a problem. Each character’s dialog should be so distinct that even if you took away the dialog tags, the reader would still be able to tell who was speaking. If you can take one character’s lines and give them to another without rewriting, that’s a sign that your characters don’t have distinct voices.
One way to ensure your characters speak differently is to mentally cast different actors in the roles. If the president is played by Helen Mirren and her top general by Harrison Ford, they should “sound” different.
If you’ve never done drama yourself, grab some writer friends and try reading some scripts aloud. Doesn’t have to be Shakespeare, although it could be. Notice how the characters’ dialog differs and how you tend to change your reading in response.
Diction—that is, word choice—is one of the most important aspects of dialog. President Mirren might speak of “reaching an agreement” while General Ford speaks of “building consensus.”
Match voice to personality
A reserved person will usually be terse, whereas an outgoing person will be more verbose. Introverts process before they speak, so their words are carefully chosen. Extroverts often need to process by thinking out loud, talking through a problem, which means they may blurt the first thing that comes to mind.
A person who is analytical will speak in concrete terms of things that can be measured and evaluated. A creative person will speak in abstracts of things that are difficult to quantify.
Level of education and place of origin also strongly affect how a person will speak. A college graduate from Atlanta will speak very differently from a high school dropout from Brooklyn. That said, the dropout could choose to educate himself into a better vocabulary, and the Atlantan might retain a down-home dialect so as not to be seen as putting on airs. The words you put in your characters’ mouths reflect their character—and vice versa.