"Not in our arsenal of snappy comebacks." - Walter
So let's say you grew up bookish and introverted. (Like me. Yay! Friends!) You probably read whatever you could get your hands on. I know I did. I vividly remember helping myself to a Reader's Digest my family had lying around. Good stuff. Some of it was a little deep for my age then, but I got the basic idea. Reading "Mike's Flag" and something that was like a Bieber fan's guide to Romeo & Juliet possibly had an interesting effect on my taste now. (This will be important later.)
Naturally, when I discovered that the Wilson County Public Library's Bookmobile* rolled around to my neighborhood every couple of weeks, I thought it was pretty cool. Crammed into a small bus that would probably send my current 5 feet 9 inches self into a claustrophobic panic attack, were, well, books. They had whatever I might be interested in, which at the time included The Babysitters Club, Goosebumps, and American Girl magazine.** Anything else that might be a ghost story was also welcome.
I grew up in the 90s. In that decade and the one previous, there was a wealth of kids' books that were available (but never required for me...ah the miracles of private school.) Now, granted, kids did slack off reading for a while there, but there were more readers than the intellectual elite would like to admit.*** (Why do you think The Babysitters Club was so popular?) This created a generation of kids who are quite intelligent and possibly a tad apathetic about academia (or, if they're like me, inwardly ambitious, painfully procrastinating, and somewhat snarky.)
All this boring intro actually has a point, so stay with me.
Let's say that after a crash course in Narnia, you graduated on to greater and higher works of literature. Great. So you're all up into some Austen and some Stoker and maybe a little Melville, all shunning the television in your quest for academic and philosophical greatness. So after you take a break and pull your pasty head out of the wood-pulp, you find after some assignment or such that you enjoy writing, shoot, that it's downright awesome. Not content to stick with mere poetry with its paltry sound devices and subtle imagery, you try your hand at writing some short fictional stories. Then the biggie. The novel. Yours is a high and lonely destiny, writing such works of intellectual amazement. Triple syllable words and old-fashioned ideals are reanimated, lurching across the page like so many undead.
And your dialogue's probably terrible.
But what? You're well-read! All writers should read widely. You've done it all right. You've read the classics and the manuals and the instructions on plot and characters and setting and structure.
You don't get to know a person based on their surroundings. Nor is any person likely to hand you a paper when you meet them that lists things like "sarcastic" and "nice." Description can only take you so far. I have brown hair (most of the time) and blue eyes (all the time.) No matter how long you dwell on what I look like, you will never know me. When I open my mouth, you'll start to get to know me.
Dialogue will tell you most of what you need to know about a character. Actions are helpful, but if your dialogue is stiff and formal (when it doesn't need to be,) well, that's a turnoff. Your characters aren't natural. But you've read all those books!
Watch tv. Or a movie. Maybe you could listen to how people talk around you.
Yeah. I said it. If you want to know how to write good dialogue, you have to hear it first. A good television show to start with is The Office. No, really. Drama is too much, and comedy not enough, but The Office is just about perfect. Conversations on the show flow at a natural pace, and that's what you're looking for. As far as movies, I'd shy away from the new Star Wars trilogy, but the original three movies are for finding some amazing banter and such. (Han and Leia, obviously.)
So now you've got your characters who talk like normal people. Their words move with a wonderfully accessible rhythm. But please refrain from...
The Campfire Tale.
One of the mechanical faults that I will now criticize the Twilight books for is that some characters start talking.
And don't stop for several pages.
This really isn't seen much until you get to know three of the Cullen "siblings." One's like "Eh, my family put me in an insane asylum and told everyone I was dead. *shrug* How ya been, I'm feelin' Italy, how 'bout it?"
And then you get stories from the blond sister and brother. She is not as long-winded as he is. This guy tells this story about how he was a Confederate soldier (and apparently the actor has amazing accent power in the film) who went to Mexico, and vampireness, and blah blah blah. Ya boy talks for like a whole chapter. There's never any interaction with other characters, except the in-narration dialogue (not realistic, really.) And at the end of it all, the rest of the Cullens are doing other stuff, like cleaning up the kitchen and manicuring their nails out of sheer boredom. Dang, dude, you coulda just said "This Mexican chick turned me. I met my wife in a bar the next century, and then we came here. Nice town."
Do not have your characters go on and on and on with no interruptions or questions. Your work requires dialogue that's smooth and flows. Too much talking from one person, and your novel takes on the tone of a wiki. Not cool.
*I think they don't run the Bookmobile anymore. This is sad, because for me, it was like mini-Christmas every couple of weeks.
**Don't laugh, I watched the end of Red Dawn and followed it up with 27 Dresses. I'm all eclectic like that. Or just, you know, human.
***I did not read a Newberry book until A Wrinkle in Time when I was in high school. Seriously, those award winners aren't popular among the kiddies. They're picked by teachers who probably cry over them and pick them because of that. I don't want to read sad junk now, and I especially didn't when I was nine.