People cannot help but comment on what they see as they judge their surroundings. This reveals the setting of the story.
Gosh this room is so messy, I don't understand how you can find anything in here?
We know we’re indoors, in a room, looking for a particular item. The room is full of clutter. We are not alone.
Lovely weather isn't it, neighbour?
We know we’re outside. We spot the neighbour. We picture a blue sky and sun on our face. Is he trimming his hedges by any chance?
Is that apple pie I'm smelling?
We’re indoors, probably near a kitchen. We’re not alone. We’re hungry.
Using dialogue and setting to establish contrast
Example: The rain had soaked her clothes, her hair stuck to her face. Mary grinned, she was positively glowing. 'I love you too.'
The cold wet weather contrasts with the warm fussy feelings of love.
It was all blue skies and sunshine that Monday morning. Jack's next door neighbour's kid came racing past on her bike. 'Morning mr. Morgan!' the kid next door shouted, waving happily. 'Fuck you.' Jack answered under his breath as he smiled and waved back.
The lovely weather and polite cheerful neighbourhood kid contrast with Jack’s foul mood.
'No child of mine is gay.' said Mr. Johnson. 'I raised you better than that.' 'I am though dad.' Thomas took Benny's hand. 'He's... my boyfriend.' Benny squeezed his hand. 'You best stop that nonsense right now Tom.' Mr. Johnson. 'You know damn well we don't tolerate that kind of nonsense in this house.' 'It's not nonsense!' Thomas shot back. 'I love him.' 'No you don't!' Mr. Johnson shouted. 'Not if you want to live in this house, you don't!' 'That's all right.' said Benny calmly. 'He can come live with me.'
This example shows who is who. The contrast in opposing values is made crystal clear as are the problems they create. We understand the motivations of each character enough to know what facial expression is likely on Mr. Johnson’s face as he disagrees with his son. The expression on Thomas’ face as he is kicked out of his parental home needs no description.