Lighting

The key light should have a source inside the scene. Contrast and warm/cool choices also change how relationships read.

Name the source of the key light when you can: a window, a lamp, a screen, or the sun.
Brighter, flatter high-key lighting tends to feel safer, more open, and more commercial. Darker, higher-contrast low-key lighting tends to feel private, threatening, or dramatic.
Warm tones often suggest intimacy or memory. Cool tones often suggest distance or control. A hard warm/cool split in one frame is often read as a split or confrontation in the relationship.
When the dramatic turn happens, let the light change with it: a cloud passing, a lamp switching on, or light entering through a door crack is more executable than writing “the emotion flips.”