Making Dialogue work, or, "Wha 'choo talkin' 'bout, Willis?"

I've found that good dialogue tells you not only what people are saying or how they're communicating but it tells you a great deal - by dialect and tone, content and circumstance - about the quality of the character. - E. O. Wilson

Let's talk about your characters. You, yes you... with your pen in hand, preparing to scribble down the next scene in your ongoing masterpiece. And you, with your keys poised over keyboard, eyes squinting over your last bit of writing to check for errors in grammar and syntax. Put down your writing utensils, whatever they may be, and come join me in a circle. Yes, that's it. Mind you don't sit on someone's hand. There, that's better.

Now, your characters. How do you feel about them? Let's pick one in particular. You know the one I mean. The one character that you can't seem to get out of your mind. Whenever you have a free moment, and life lets you stop for a moment and reflect upon your day or even your hour, that character, that one fantastic character that you've dreamed up and brought to life like a literary Dr. Frankenstein comes to the forefront of your mind and you begin to play with him or her. You imagine again how she looks, blonde hair, full but slightly damp around her face as the bright sun causes her to sweat a little. Or perhaps you imagine him, bare chested, white cottony pants, standing in prosaic pose at the helm of a sailing boat, skin tanned, full hair blowing in the crosswind. You know her personality, you know his mannerisms. And not in just some flippant, peripheral way where you learn their name and forget about them. You know them. Now comes the tough question: Do your readers know them?
I don't mean the normal, mundane knowledge one might gather from a casual perusal of your tome. I refer to the intimate knowledge. Do they know your character like you know them? To put a finer point on it, do you let them know? There are many ways to let your audience in on the grandness of your favorite character. Actions, description... and most importantly, Dialogue.
We humans learn a lot about a person from that person's speech patterns. Think of your character, and how she speaks. Does she pepper her language with obscenities? Does she try to impress her friends with large, flowery words? Or perhaps she just tries to be herself, and speaks plainly. Using dialogue and language, you can convey your character's personality in a way that pulls the reader in. But you must be careful: Improperly using dialogue can have the opposite effect.

Here are some do's and do not's to help you out:

Do Not overuse slang when writing dialogue. If your reader has a severe accent, you'll want to relay that and it's understandable to reflect that in dialogue. However, overuse of this slang makes the reader have to work hard to understand what it is your character is trying to say. I suggest instead to make mention of it, and how the listener reacts to it first. Perhaps give some hint of slang, but don't deluge the reader with it!
Do be concise with your dialogue. Dialogue is the salt of your book. Use it to good effect, but don't try to throw voluminous amounts of it at us!
Do keep each of your character's talking style separate, especially when they're talking to each other. Readers use cues in their speech patterns to differentiate between two or more speakers, particularly in a long conversation.
Do be careful with dialogue attribution. Yes, I'm sure you've heard this before, but it bears repeating. "He said" and "She said" works for 99% of your cases. Leave Tom Swifties to the amateurs, you're better than that!

I usually give examples of what I'm talking about, but I think I'm going to do things a little differently this time around. Over the next few posts, I'm going to post "Interviews" with my book's characters. Yes, It's unadulterated self-promotion, but it's also a great way to show how dialogue can help define your character, and how honestly cool it is to have different dialogue flavors work for you throughout your book. So, stick around, and in a couple of days you'll meet my favorite characters!