Anna smiled a little wider, showing gums. “So that was weird today.”
“I know, right?” Dionne perked up, edging forward on the bed, “Teacher's never been so vague before. Not about any of my stupid botany questions, and I've been asking them for years.”
“Right,” Anna nodded curtly, “Or any of our questions, really. Just last week I stayed after class to grill him about the engines Egerians use on the distance-ships. And Weston, you're always giving him a hard time about . . . ah, history, isn't it? That's your specialty?”
“Mmm,” he said thinly, “What's your point, Anna?”
And so on, and so forth.
The problem wasn't merely that this dialogue was filled with needless dialogue tags and adverbs--though that certainly sticks out to me now. Nor was it necessarily that I was using dialogue as a means to infodump, though, as you know, that's a problem, too. The big issue here is that the characters all have essentially the same motivation--discussing that morning's events--and so their conversation circles the same issue over and over again without much spark or realistic life.
In the five years (and seven completed manuscripts) since I wrote that passage, I've made it my job to study crackling good dialogue. After picking apart interesting conversations on television, in the pages of my favorite books, and among the fascinating human beings around me, I've discovered one essential truth about communication:
Each speaker converses primarily with him or herself; communication is only ever a coincidence of overlapping motives in a given moment.
In any scene, your speakers must each have their own motivation and goals--and, though these motivations and goals might sometimes collide with those of your other characters, for the most part they will be disparate for any group of people greater than one. This is more easily illustrated then it is explained. Observe the following scene from the BBC's Grandma's House (NSFW and younger readers for some adult humor and language):
In this scene, Simon's mum, Tanya is primarily concerned with defending her parenting and her choices in her divorce. Simon, meanwhile, is attempting to communicating his new enlightenment and how it has impacted his view of his childhood. The dialogue is snappy and interesting because it's so fundamentally at odds. When Tanya asks direct questions, Simon responds not by answering them but by reiterating his own prevailing goals (reiteration of the philosophical lessons he recently learned at a motivational retreat):
Tanya: You didn't speak with the bastard, did you?!You can imagine how such an exchange might have been handled by a less competent writer. Perhaps Simon would have imparted a straight description of the event, and Tanya would have asked questions about it. When Tanya asked about Simon's father, it might have gone something like this:
Simon: You can't move forward with your life until you're complete with your past.
Tanya: You didn't speak with the bastard, did you?!
Simon: I did. I'm feeling much better about him now that I attended this seminar.
Tanya: (thinly) Mmm, what's your point, Simon?
Simon: I learned at the seminar that you can't move forward with your life until you're complete with your past.
And so on. But the dialogue that's there is much snappier than that. It moves quickly, and because the characters are each essentially talking to themselves--with moments where their interests happen to intersect, before they move apart again toward defensiveness or anger or frustration at the other party for refusing to listen--we breeze through it. As much is told in the logical gaps that exist between lines as it is in the lines themselves.
Most importantly, this dialogue is lively. It moves and it sparks. Now, when I sense that my own dialogue has begun to grow stale, I remind myself of each character's essential goal. Very rarely do realistic characters just want to "discover information" or "discuss the day's events." They want to prove themselves, defend themselves, impress others, look attractive, absolve themselves, or do any number of other things that real human beings might be attempting to achieve at any moment. And because real human beings are so diverse, these interactions are often contentious ones.
Conflict is at the heart of conversation. And if you keep your characters' motivations at the forefront of your mind, it should be at the heart of dialogue, too.