If you are not familiar with the concept of blocking, it comes from stage direction, but also applies to writing. By "blocking" I mean understanding where your characters are in relation to each other.
When I was in plays in high school, we'd often mark the stage with an X to indicate where certain actors were supposed to stand to deliver their lines. This shows them in relationship to the other characters and (in the case of high school drama) prevents the actors from forgetting where they're supposed to stand when they walk on stage in a blind panic.
This also applies to writing in that you, as the writer, have to put those Xs on the floor for your characters and know where they are in relation to each other. The next step is to make sure your readers also know where your characters are at all times and where they are in relation to each other.
If blocking isn't used in a novel, all you end up with is characters who stand around in a void (or worse, a white room) and read lines to each other. This is boring.
Instead, use blocking so we can envision where the characters are on the stage and how they’re moving around and with each other. They need to move, gesture, pace, or whatever a normal human (or green-eyed monster) would do in that situation.
All that being said, this movement needs to make sense. If they stand, then they need to sit before they can stand again. If one character is pacing, and the other one stands to pace as well, there needs to be a good reason or else they'll be chasing each other around the room.
As with many of the posts in this blog, careful thought needs to go into what you're doing with your characters. Do a blocking sweep on your novel and make sure the characters are all moving in ways that make sense, and, most importantly, make sure they are moving in general.