1. Reveal and explain character.
a) Who speaks - this must be clear..
b) What they say should be relevant to the story
c) How they speak should be distinctive for each character.
2. Advance the action - within each scene and within the novel.
3. It must create conflict.
a) Between the protagonists.
b) Against a character’s own inner thoughts.
4. Provide information - background detail or motivation.
5. Add pace and suspense through giving pointers, and vary the rhythm of the book.
6. Show viewpoint, emotion and mood.
7. Show inner thoughts alongside or instead of speech - But does it reveal everything, or only a part? What is not told?
8. Weave essential detail and action in with the dialogue. Great blocks of research
interrupt the flow of dialogue and readers tend to skip it.
9. Dialect and historical slang. Absolutely no gadzooks type of speech. Aim always for straightforward clarity. Where it is necessary, don’t overuse - Make it fit the speaker and period. It’s safer to use only one character if a particular way of speech is needed to add the right sense of place.
10.Dialogue should add sparkle and life, colour and tone.
An ear for dialogue is important in any story. If you don’t have it, acquire it. Listen and take note verbal patterns, body language, what is left out or not explained, punch lines, how people who know each other well need fewer words. How people interrupt, discuss two subjects at the same time, get at cross-purposes. How people argue and react to confrontation. The gender divide - men and women differ in conversation, in what way? Listen to puns and syntax, dialect twang, regional idioms, favourite sayings and old saws. Notice how class, occupation, age and character are revealed in conversation. Listen also for the effect of emotion: Frustration. Anxiety. Anger etc.
Most of all, keep it brisk, clear and to the point. If it doesn’t have a purpose, take it out.
Exercise: If you have trouble writing dialogue, take a piece of your own narrative, the aim of which is get across certain information to the reader, and rewrite it as dialogue which will impart the same information in a more interesting way. Show what the characters are doing while they are speaking, and how they feel about what they are saying.