One of the most-repeated lessons of writing workshops is that your characters should have different voices. I have been struggling with that (euphemism), but I was impressed by the unwitting demonstration Tad Friend made of the power of dialogue in his recent New Yorker article about Pixar's first live-action movie.
The movie in question, called "John Carter", features Friday Night Lights heartthrob Taylor Kitsch in the leading role, and if Friend's quotes are representative of Kitsch's usual way of expressing himself, the actor uses the f-word a lot. He uses it in just about every single one of his sentences, as a matter of fact, while none of the other interviewees - Andrew Stanton, the main focus of the profile, and Kitsch's partner in the movie, Lynn Collins - even got close to pronouncing that sort of profanity in front of the journalist. (Stanton uses a b-word, about Disney, in the sentence "Disney... won't, history tells us, have the b---- to commit", but no f-word. Gotta have values in life.)
So it was a testimony to Friend's good writing, which highlighted the protagonists' different voices, that when I reached the last column of the article and read " 'It still makes no f------ sense to me, but this is how we do it,' Stanton said" (except that The New Yorker did not censure the f-word), I knew for sure someone at the magazine had let a mistake slip by. This is not Stanton's voice, but Kitsch's.
Some fiction-writing instructors like to mention 3 Vs in creating distinctive voices: vocabulary (pet words), verbosity (erudition, length and construction of sentences) and velocity (pace, speed of elocution). The Gotham Writers' Workshop occasionally runs free writing classes at my favorite bookstore - McNally-Jackson in SoHo - including a dialogue writing one. I've never attended the class, but anything that happens at McN-J has to be good.
I think one of the reasons I've had a hard time writing distinctive voices is that I only write dialogue I feel I could speak. (I often read my dialogue aloud. And my non-dialogue. Although Gustave Flaubert has been advocating this method since the nineteenth century, I owe it to Garrison Keillor's Good Poems to have finally prompted me to take action; once I got started with [reading aloud] poetry it was easy to transition to fiction.) I use breath a lot to figure out when a sentence is getting too long for a character to say, but for my next book I should also make more of an effort to vary words and pace instead of simply making the conversation believable to the reader.
I do wonder if Kitsch will ever stop peppering his sentences with the f-word. That would certainly show an evolution (growing maturity? different self-perception?) in him. An outer change in dialogue reflecting an inner change in the character: that would be the best dialogue lesson of all.