Arianne "Tex" Thompson gave a writing workshop in Austin in July of 2017, titled "The Plate Tectonics Theory of Dialogue". It looked at dialogue through the metaphor of plate tectonics: your characters are constantly in motion, constantly changing. They clash, collide, fold, buckle, shift. Good dialogue expresses all that.
What not to do when writing dialogue
Characters speaking bad dialogue often
-- ping-pong (always take turns speaking)
-- speak only in complete sentences
-- finish every thought
-- address every point directly
-- move through conversation in strict linear order (no deviations, no surprises)
-- inadvertently reveal the author's hand ("As you know, Bob", "What do you mean by that, Socrates?", "This sounds like something out of a bad movie" (Dischism -- a phrase attributed to the author Thomas M. Disch)
This is a second workshop by Tex Thompson that I have been to. The first one was the "Escape from Clichea" fantasy worldbuilding workshop that Tex Thompson gave at ArmadilloCon 2016 (a local science fiction convention). I found it very helpful, entertaining, and full of practical, doable advice. Here is my blog post on Tex Thompson fantasy worldbuilding workshop.