When developing characters, my goal is to develop a distinct voice for each. I consider voice, cadence, slang, dialect, and word pronunciation. For example, in a chapter book I’m still tinkering with, one of the characters has a lisp due to missing front teeth, so some of her words become slurred. “Great” becomes “gweat.”
The tone of voice is a consideration. Tone can be serious, funny, formal, sarcastic, cheerful, or any other attitude. In my picture book, The Munched-Up Flower Garden, Liz is excitable and upset. Her attitude is expressed through dialog and actions.
Cadence is the rhythm of the text. Does your character speak in long or short sentences? Another character I’m currently developing uses more sophisticated words than his friends. These elements give characters uniqueness.
Think of each character as a real person and remain consistent throughout the story with his/her particular speech patterns. Word choice in speech reflects the time in history. If characters are contemporary, they use language that reflects today, but if they lived in the 1920s, their word choice should sound differently than that of modern-day kids.
Realistic dialog makes characters seem real and adds appeal to their personalities.