Bell does a wonderful job of breaking dialogue into eight essential characteristics. One of these is to make your dialogue full of subtext. He explains that dialogue should be like an "iceberg",the part we read on the page and the part underneath the surface. There should be layers beneath the surface of story,character,and theme.
1- What has happened in the story so far will affect the present. This is the back story...whether it's presented in the story or not it should effect the dialogue.
2- It's important to "know your character's deep background-the events that shaped her from childhood on." In Susan Collin's, Hunger Games,we don't fully understand why Katniss is so curt with her mother until later.
3- Often writers say that theme doesn't emerge until much later in the writing process. So once your themes have shown themselves you can go in and tailor your dialogue. Then when the reader discovers the theme, the conversation is more meaningful in retrospect.
Bell, James Scott.Revision and Self-Editing:Techniques for Transforming Your First Draft into a Finished Novel.Ohio: Writers Digest Books,2008.
So now you know what I'm busy working on. What's on your plate today?