Dialogue is the heartbeat of any fiction novel. An author can use the verbal interaction between characters (or a character with itself) to flesh out those characters, build suspense, explain elements of the story, bring in back-story, and entertain the reader … if it’s done right.
Do base your characters on people you know (or know of: like movie stars). If you want to be the inspiration for the hero or heroine, that’s fine; as long as you have (or can create) the needed heroic qualities.
Do use dialog to bring clarity to your story: reveal facets of your character, explain plot history or setting, and build emotion in a scene. Using dialogue for these is much better than blocks of expository text; which tend to get boring quickly.
You can also accomplish multiple purposes through the use of dialogue. For instance; an argument between your protagonist and another major character can reveal character facets like temperament, education, and the motivations of both characters. Brief insertions of actions (she flipped her long, blond hair out of her eyes, then continued…) can also accomplish describing your character more efficiently than some long gaze in a mirror.
Do allow your characters to express themselves naturally. Their speech is part of their personality.
Do keep a log of each characters pet phrases and speech idiosyncrasies.
Do practice dialogue with each character. As a writing exercise, set up a scene with the character of the moment and let them speak. Your characters will develop as you become familiar with them. Letting them build in your mind through practice dialogue will save you having to re-write previous scenes because your character changed
Don’t insist on formal grammar and sentence structure. Few people actually speak like a formally written document. Maybe when giving a speech, but not in conversation. Use natural language.
Don’t include boring details of a long conversation. People do sit around and chat about the weather and politics, but unless these are directly relevant to the story or used in some meaningful way, cut away from the scene with a statement like, “They discussed the weather for a while”. Leave out the fluff and avoid miring the pace of your story.
Don’t change POV during a discussion. If you want to reveal the thoughts of the non POV character, these need to be revealed by subtle action and being recognized by the POV character. “Susan saw anger in Michael’s eyes though his voice remained calm and measured.”
Don’t let your dialogue get trite of stiff. You destroy the believability of your character when their interaction degrades in this way. If you feel it getting trite, go back and study your characters real-life model a bit more and see how the would handle the dialogue in question.
Don’t copy anyone so precisely that you get sued for basing your villain on some well known politician. Base your character, don’t make them a copy of.
Don’t over-use dialogue tags: said, replied, asked, etc. Use these for the first couple of rounds in a conversation to distinguish who is speaking, but unless you’ve got a crowd of people interacting all at once, let the conversation flow naturally.
Don’t use adverbs in language tags at all. Instead of ““What do you mean by that?” Angela asked angrily” use ““What do you mean by that?” Angela’s eyes flashed with anger.”
Show, Don’t Tell
An old writing axiom tells us to show the reader what is going on, don’t describe it to them. Dialogue is a great way to do this. It can be entertaining, informative, and revealing all at once.