"Dialogue? Isn't that just talking in print?"
The answer is both yes and no. Actual speech might look like this:
"Well, I was thinking about going, but, you know, it's really not that nice out today, and like, I have this term paper, and, um,...
"Real speech is full of starts and stops and sounds and meaningless "filler" words, such as: "like" and "well" and "you know." Occasionally sprinkling in some of those words and phrases can add some flavor, but readability suffers from adding too many.
Dialogue is purposeful and streamlined.
Dialogue in fiction needs to have a direct purpose. Each conversation should play a meaningful role in the development of the plot, and though speech should sound authentic, written conversations may need streamlining to keep from becoming tedious to read.
Dialogue should illustrate character and the relationships between characters, but ideally, it should also move the scene/story along.
This conversation is superfluous:
"Well, it might rain," Mia said.
"Yeah, but that's OK," Allen said.
“We can still go if it rains."
"True, but we'll get wet, and that won't be much fun."
"Hmm. You're right."
I learned almost nothing in that snippet. Mia and Allen talk about the weather, but then they tell me that the weather doesn’t even matter (so why did I have to read about it?) There's no tension, little relationship development between the characters, and the characters aren’t very distinct. As a writer, I wasted my dialogue, one of my most-powerful writing tools, on nothing. If I do that often enough, readers will lose confidence in me.
Now the same scene with some story-purpose:
Mia looked up at the storm clouds blowing in. “It’s gonna rain."
"So?" Allen asked, untying the skiff. "We aren’t afraid of a little rain, right?"
"Dad said not to go if it rained."
"Oh, come on. It's not raining yet, and we’ll only be gone a few minutes," Allen said. "We’ll be back before your dad even knows we're gone."
That scene moves the plot along, and in doing so, it tells the reader what the characters said, what they did, a bit about the personality of each character, and the dynamics of their relationship.
Dialogue should have clarity, grounding, and balance.
Tags. "Mia said," "Allen asked," are examples of speech tags. Tags clarify who said a line of dialogue.
Here's an example to work with:
"Promise?" Mia asked.
"Sure. I'll row fast," Allen said.
The clouds threatened, dark and full, promising a downpour.
"I haven’t seen any lightning."
"Me, either. And that's what’s dangerous, right?"
Several things could be improved on here.
Clarity. A reader always needs to be clear who said a line of dialogue. It would be fine to start dropping some tags once a pattern is set (Mia-Allen-Mia-Allen), but by introducing the clouds as a subject of a sentence, I've broken the pattern and need to reset it.
"Promise?" Mia asked.
"Sure. I'll row fast," Allen said.
The clouds threatened, dark and full, promising a downpour.
"I haven't seen any lightning," Mia said.
"Me, either. And that's what's dangerous, right?" Allen said.
Placement. Though I've now made it obvious who's talking, the tags are in the same place—at the end of the dialogue. That makes the passage stale, and also, the last thing in any sentence or paragraph receives an extra punch, because your eye takes that slow beat, moving down to the next line. So, it’s a waste to give a tag that great “punch” placement, over and over.
As an example, I'll move Allen’s from the end of his dialogue to the middle.
"Promise?" Mia asked.
"Sure," Allen said. "I'll row fast."
The clouds threatened, dark and full, promising a downpour.
"I haven’t seen any lightning," Mia said.
"Me, either," Allen said.
"And that's what’s dangerous, right?"
Grounding. In the above example, the characters seem to be just voices hanging in space. You can ground your dialogue by integrating it with action, gesture, or thoughts.
Mia is making a change of thought in this scene; she goes from not wanting to take the boat out, to agreeing to do so. You can use thoughts to show that process.
Dad would be furious that she'd forgotten his tools on the island. If she could get them before the rain started...
"Promise?" Mia asked.
"Sure," Allen said. "I'll row fast."
The clouds threatened, dark and full, promising a downpour. But not yet overhead.
Maybe Allen was right. Maybe there was time to get there and back. "I haven't seen any lightning," Mia said.
"Me, either," Allen said. "And that’s what’s dangerous, right?"
You could also ground the scene with action, gesture, or setting. "Promise?" Mia asked.
"Sure," Allen said. "I'll row fast."
Mia looked up. The clouds threatened, dark and full, promising a downpour. But not yet overhead. Maybe Allen was right. Maybe there was time to get there and back.
"I haven't seen any lightning," Mia said.
"Me, either." Allen climbed in, the skiff's boards creaking under his feet. "And that's what’s dangerous, right?"
Balance. You can use a variety of tools to keep clarity (setting up a pattern, tags, attributed gestures and actions and thoughts). It’s important not to bury the dialogue in these, however. Look at each interaction and decide what is the most important thing in that interaction and be sure that is the star.
Here’s an example of burying the dialogue:
Mia looked up at the clouds blowing in. "It's gonna rain," she said, walking to the edge of the water and looking out over the glossy, gray surface to the tiny island way off in the distance.
Too much information in one pass and everything is diluted. The fact that she knows it will probably rain is the most important element to that paragraph.
So in taking the whole thing together, here’s one example:
Mia looked up at the storm clouds blowing in. "It's gonna rain."
"So?" Allen asked, untying the skiff. "We aren't afraid of a little rain, right?"
"Dad said not to go if it rained."
"Oh, come on. It's not raining yet, and we'll only be gone a few minutes."
Allen pushed the skiff to the edge of the water. "We’ll be back before your dad even knows we're gone."
Dad would be furious that she’d forgotten his tools on the island. If she could get them before the rain started.
"Promise?" Mia asked.
"Sure. I'll row fast."
The clouds threatened, dark and full, promising a downpour. But not yet overhead.
Maybe Allen was right. Maybe there was time to get there and back. "I haven't seen any lightning," Mia said.
"Me, either." Allen climbed in, the skiff's boards creaking under his feet. "And that's what's dangerous, right?"
A conversation is an integrated experience. It can include what’s said, what's thought, a character's emotional state, action, setting, etc. Used effectively, and as part of that whole experience, dialogue can be one of your most powerful writing tools.