You'd be forgiven for thinking that in order to write realistic dialogue you need to write as people really speak. Ironically, this is not always the best practice when it comes to dialogue.
This is just a quick guide with two really important tips that I believe can improve your dialogue overnight. There is of course much more to writing dialogue, but this is a great starting point!
In real life, we talk TOO much
Let's try an exchange between Joe and Sarah. They're talking about what to have for dinner. I'm going to pass over all the prose and exposition, and get straight to the dialogue for now. After the dialogue, we'll talk about if/how it works, or doesn't work.
REAL LIFE DIALOGUE:
JOE: Sarah?
SARAH: Hmm?
JOE: What do you want for dinner?
SARAH: Dunno. What are you thinking of?
JOE: Dunno. Can't decide.
SARAH: Pizza?
JOE: We had pizza the other day.
SARAH: True. Pasta?
JOE: Yeah we could have that. Oh no wait, we ran out yesterday.
SARAH: We could order a Chinese then, if you want.
JOE: Yeah, we could do. Do you want to call them?
SARAH: You call them.
JOE: Okay, where's the menu?
SARAH: Drawer on the left in the kitchen.
This exchange is overlong and boring when you're reading it. Imagine this exchange with all the additional prose that shows the mood, facial expressions and movements within it? This could potentially take up PAGES. Your readers will fall asleep!
REALISTIC FICTIONAL DIALOGUE
JOE: What do you want for dinner?
SARAH: Maybe pizza, or pasta?
JOE: We had pizza the other day, and we're out of pasta.
SARAH: All right, what about Chinese?
JOE: Sounds good.
Now, this rectification wasn't about making award-winning dialogue. The point here is to show that Joe and Sarah can't decide what to eat, and after some deliberation, decide on Chinese food, and that you can get the point across much quicker by cutting all the 'real life' fluff out.
DOES THE CONVERSATION EVEN NEED TO BE THERE?
For a conversation so banal and irrelevant to the plot (in this example, anyhow!), you could even cut out the dialogue almost completely and inform the reader via a short bit of prose:
Neither of them could decide what to have for dinner; the pasta had run out, and they'd already eaten pizza earlier that week. Eventually, Sarah suggested a Chinese takeout.
"Sounds good," said Joe, standing up to fetch the menu from the kitchen.
The "Ellipses Curse"
The only reason for an ellipses is if there is an omission of words. If a character trails off in surprise or loses their will to speak, you might end the sentence in an ellipses:
"I just..." Sarah's voice melted into a sigh as she struggled to find the words. "I don't know what to do. I'm so tired; I've been at work all day."
A mistake many people make is thinking of real life chatter when writing it in their novel. In real life, people pause to take breaths out of pace with what they're saying, or they pause for dramatic effect. In text, it doesn't translate well and tends to force a pause where the reader may not want one.
"I don't know what to do... I'm... very tired... I've... been at work all day... " Sarah said.
I'm not here to stop anyone doing this - but for me personally reading an abundance of misused ellipses makes the dialogue's flow come to a halt, and makes it harder to read than it needs to be.
In standard punctuation, a natural and well-flowing pause is indicated by correct usage of commas, full-stops (periods), hyphens, semi-colons and even colons. If you can, learn to use ellipses only as a means to fill an omission. Your dialogue will thank you for it!
The above guidelines can be applied to almost any area of dialogue in your work. If it's not plot relevant, you could easily skim over it with some prose (or cut it out entirely), and if your book has more than a couple ellipses per chapter you might be overusing them. Happy writing! <3