Just an interesting article on writing dialogue I thought was worth a read. One observation of my own regarding Bunting’s “real people refuse to repeat themselves” point: real people also DO, in fact, repeat themselves. Not, per se, when asked to, but in the course of a story they tell or in how often they tell the same person the same story, people repeat themselves more than they realize. That said, you don’t necessarily want to over indulge on this element in your character’s dialogue, because that can get annoying–unless, of course, that’s your point or it’s your intent to convey that. Just something to factor in that, yes you want believable dialogue, but some things our brains naturally brush over in real life and therefore doesn’t translate well to the content of a novel.
It’s a delicate balance, but Joe Bunting, “The Write Practice,” writes a good article here with a lot of great insight to think about.