I try to vary my framing of the shots. Just because people are talking doesn't mean I just have to show their faces. I sometimes draw panels in which the entire body of the character can be seen (it helps with body language!), I sometimes zoom out so that ALL participants in the dialogue are in the same panel, I change angles, etc., etc.
I also try to make sure that I have actual backgrounds in at least one panel per page; it helps establish a sense of place, and give context. It tells the reader that all of this isn't just a bunch of disembodied heads talking in a void; it's taking place in an actual location. Also, the walk-and-talk thing is good too. A lot of my text-heavy scenes have taken place with my characters moving from one place to another, which means I can draw them walking through various landscapes.
But yeah. Pull the camera out to show more of their bodies is a good first step. People don't just talk with their faces - they speak with their whole bodies. People gesture with their hands, hunch their shoulders, stand up straight, wave their arms, etc, etc.