You've got to have THAD!

When  editing your work-in-progress, check carefully scenes containing dialogue. If two characters are speaking, you can often avoid tags (he said, she said), but you must not have talking heads.

That's why it's important to consider a Talking Head Avoidance Device.

What is thad? It's just about anything you can think of to keep your characters doing something while talking. They can be fixing a car, chopping vegetables, drinking coffee, jogging in the park, changing diapers, planting a garden, but they must be doing something or you risk scenes with talking heads.

In addition, make sure your dialogue isn't On the Nose. Dialogue usually contains Subtext and that's what makes the scene important to the story.