Like the contents of a bug-out-bag, every detail of your story should serve a purpose, and preferably more than one. This doesn’t just apply to plot points, but ideally to the individual elements and dialogue that go to make up a scene.

For instance take the introductory exchange of dialogue from the Brodys in Jaws (one of the more perfect films out there, in my opinion). The scene is their bedroom as they first wake up in the morning:

Martin: “How come the sun didn’t used to shine in here?”
Ellen: “We bought the house in the fall. This is summer. Someone should feed the dogs.”
Martin goes to the window
Ellen: “Do you see the kids?”
Martin: “No, they must be in the backyard.”
Ellen: (affecting a New England accent) “In Ahmity you say ‘yahrd.’”
Martin: “They’re in the ‘yahrd’, not too ‘fahr’ from the ‘cahr’. How’s that?”
Ellen: “Like you’re from New York.”

What does this little exchange of dialogue accomplish?

1. It establishes that the Brodys are newcomers to the community from New York and the name of the community they’ve moved to: Amity

2. It establishes they have kids and are overall a comfortably loving family, as they immediately address simple domestic matters upon rising

3. It hints at the quiet, safe nature of the community: they aren’t concerned that they can’t immediately see their children outside.

4. It establishes the easy, affectionate relationship between the two, as they trade the gentle joke about accents back and forth (which also indicates they feel a little conspicuous as newcomers).

5. It hints at Brody’s conscientiousness, as the first thing he does is to check for his kids.

6. Finally, after the nightmarish opening sequence, it sets a lighter and more relaxed tone to act as a counterweight (these two tones will act in counterpoint throughout the film)

Number two, by the way, is important: it isn’t enough to say that your characters are married. What kind of relationship do they have? Are they a real domestic team, or is one or the other checked out of that aspect of life? Do they trust each other? Are there any serious problems hanging over them?

Having them address simple, small domestic chores – i.e. feed the dog – is a signal to the audience on these points. You could do it several ways.

-Ellen might wait to remind him of it after they’ve fully woken up and she can be sure of his attention, evincing an unspoken doubt whether he’ll really do it.
-This would show that he is forgetful or not always reliable.

-She might hesitate a little before broaching the topic, showing a fear of how he might react.
-This would signal he has a bad temper or is otherwise unpredictable.

-She might address it with special emphasis, as something he often neglects to do.
-This would show that he’s rather checked out of domestic matters, perhaps feels his marriage is a burden.

As it is, she mutters it in passing in the process of waking up and doesn’t even require a definite response from him. This signals to us that she at least has no qualms whatever about their domestic relationship. She feels that she can rely on him and doesn’t have to lay any especial stress on the matter. Therefore, they probably have a very comfortable and secure relationship and Martin is likely a dependable and responsible man.

It’s a small thing – I didn’t even think about it until I started writing this – but it sends the right signal to the audience about what kind of couple we’re dealing with here.

In short, the scene does three major things: It establishes the plot point that the Brodys are a recently transplanted family, the character point that they are a loving, affectionate, and responsible pair with a healthy marriage, and it asserts a new tone for the story going forward. Each of these points is vital to the film, and they’re established in seven lines that also include a bit of humor to further endear the characters to us.

Probably none of this registers consciously, but it sends signals to the audience, which will then be reinforced in the subsequent scenes.

Try to make your scenes do as much as you can. It’s usually more than you expect.