It's Sunday and I'm finishing up two scenes for today's writing quota. Both these scenes center around two characters. Both scenes share the same viewpoint character. And I will rely on parity to make sure both scenes come to life.
In very simple terms for writers of fiction, "parity" means knowing your non-viewpoint character's desire(s) and goal(s) within the scene as well as you know those of your viewpoint character.
If you feel a scene going dead, try parity. Work the scene through the non-viewpoint character's eyes. Let the non-VP character drive the scene. Your protagonist is only as strong as she needs to be to face her antagonists.
If you've ever taken acting classes, you've improvised. And if you've improvised in a scene, you know how vital it is to truly listen to and interact with and react to your fellow actor. It's a dance. Use that dance in fiction. Parity.