T is for Talking.
A character’s dialogue says a lot about him. It’s a great way to use exposition without wasting a lot of time talking about the character’s past, doing flashbacks, etc. In just a few sentences, he can tell you where he’s from and what is most important to him.
In Tunerville, there’s a marked difference between the way Chris (the protagonist) and Callahan (spirit of the Realm) talk. When Chris tries to tell people not to use the tuners, he uses very plain language—he just tells them to stop. When Callahan appears, he says, “Cease use of this instrument or there will be dire consequences.” When the two of them are talking without any tags, you can tell it’s two different people.
When I write a character’s dialogue, I think about who he is and where he’s from, and that influences my word choices. An educated character who lives in an affluent suburb won’t talk the same as someone from the sticks.
Accents are a bit different. You can’t really hear an accent when you read (not literally), so you’ll have to imply it so readers can hear it in their heads. If I make him say he’s put his wellies in the boot of the car and dammit, where did he leave his biro, because he’s got to make a list for the grocer’s whilst Emma is having a bath, then you might surmise he’s from England. You would be right. Can you hear it?
I’m not even going to try and reproduce any other UK accent here; there are quite a few. If you want to hear 14 accents in 84 seconds, watch this video. It’s the coolest thing ever.
All this applies to dialect as well, which can be written phonetically to a degree, but you can’t go overboard with it. Avoid what Margaret Mitchell does in Gone with the Wind:
“…Now, did you hear us say anything that might have made Miss Scarlett mad– or hurt her feelings?”
Thus appealed to, Jeems gave up further pretense of not having overheard the conversation and furrowed his black brow.
“Nawsuh, Ah din’ notice y’all say anything ter mek her mad. Look ter me lak she sho glad ter see you an’ sho had missed you, an’ she cheep along happy as a bird, tell ’bout de time y’all got ter talkin’ ’bout Mist’ Ashley an’ Miss Melly Hamilton gittin’ mah’ied. Den she quiet down lak a bird w’en de hawk fly ober.”
You can’t argue that it’s Southern speak, either, because only the black characters talk like that. Not only do many people think that’s pretty racist, it’s nearly impossible to read. Dialect works best when you suggest it.
Be careful not to use what many writers call Hollywood dialogue, where the character tells another person stuff they both already know. It’s clumsy. Poor writers often use it for exposition.
“As you’re aware, Robin,” said Batman, “the Joker has been a nemesis of mine for many years now.”
Probably the best thing you can do for good dialogue and characterization is go sit somewhere and listen to people talk. See if you can guess two things about them just by listening to their conversation. Try it; you might even hear something that will inspire you.