by Raelene Gorlinsky
Conversation is the way people really talk, their exact words. It may be realistic, but it is repetitive, slow, often hard to follow, often boring to others.
Dialogue is what you should put in your book - snappy, interesting, conveying important information or defining the character, moving the story along.
From You Can Write a Novel by Geoffrey Bocca: "Of all aspects of novel writing, none plays a greater con job on the reader than dialogue. The art of dialogue lies in leading the reader to think that the characters are speaking as they do in everyday life, when they are doing nothing of the sort."
Important tip: Read your dialogue aloud. Does it flow, or does it halt the movement of the story?
Dialogue must contribute to telling the story. So if your characters are talking in your head, be sure to convert their "conversation" to "dialogue".