Each scene needs some sort of tension built in. It's like the characters are pressure cookers. The anxieties cause them to tremble inside a little, and these anxieties gradually build until the characters explode to relieve the pressure. So, in every scene, ask about the characters' inner anxieties:
- Are they understandable, human?
- Are they on the way to being pressed to the limit?
- How can you show, subtly or overtly, the pressure?
- What will be the consequences of the explosion?