1) The opening sequence of Seven uses mise-en-scene like props and costumes to provide insight into the characters. For example, Morgan Freeman's character is shown alone in bed with a metronome, implying he is lonely and committed to his job.
2) Violent details like blood on the walls further the plot and suggest danger.
3) Camera shots are used to reveal character traits: a low angle shows the detectives as authorities and a wide shot of Freeman's tidy home shows him as organized.
4) Sounds like the metronome ticking and sinister music provide atmosphere and hints about future events.