When imagining a conversation between your characters, keep in mind these four speech characteristics used by actors to vary expression and add interest.
Pace, Pause, Pitch & Projection -
First, let's consider Pace -
When you are listening to your characters carry on a conversation in your imagination and you are madly trying to capture every brilliant word, think about how varying the pace of your character's words can bring interest to the story and help clarify their intent. Dialogue should not prattle on at an even pace. People don't talk that way. And those bursts of quick dialogue followed by slow, deliberate delivery adds vivid imagery to the reader and makes your characters come alive.
Consider... Pause -
Using the technique of pausing after a line of dialogue may be fairly routine and obvious, but using pause as an actor might - in the middle of a sentence - will add a whole different dynamic.
Consider Pitch -
As a writer, it may be a challenge to convey a sense of vocal pitch in dialogue, but by hearing this variety in your characters, you will no doubt discover new and interesting things to say. The fact that some characters speak with little or no pitch variance and others may be incredibly tuneful is interesting in itself. Use of vocal pitch says a lot about a person's expression and emotional state. As you write your dialogue, be aware of your character's pitch - both in general and in a particular sentence - to create variety and convey natural speech patterns. Again, finding ways of expressing varied pitch will be as individual as the writer herself.
Consider Projection -
The final "P" to keep in mind is Projection. Dialogue that is all at the same volume and delivery level gets pretty monotonous for the audience and/or reader. Using a variety of soft and loud delivery can be used to convey emotion as well as basic physical proximity. Projection is possibly the most popular and obvious choice to describe dialogue to readers.
The examples above show two very different expressions of the same dialogue, defined by projection.
Pace, Pause, Pitch and Projection - 4 tools an actor uses to find variety and natural expression in dialogue. If you, as the writer will keep these tools in mind when creating dialogue, I believe you will open the door to new creativity and dynamic expression.
Best of luck with your writing projects!
Jan Peterson Ewen