We all know that books are full of pages and pages, in turn, are full of words. But endless exposition, no matter how action packed, gets real dull fast. Dialogue is often one of the key methods of advancing the plot, as well as revealing key or subtle details that help define character(s). It can also be one of the more challenging aspects of writing. Like people, dialogue is fluid and takes on a life of its own. When used effectively, the reader should almost be able to hear the the characters speaking to each other. If done poorly, it comes off as stiff and not very believable. I struggle with dialogue. It's not an easy aspect of writing. Even after getting the conversation/scene down, I still tend to go back and keep picking at it like a scab. Yeah, I was that kind of kid growing up.
The funny thing about writing dialogue is that you actually get the opportunity to practice and hone the craft on a daily basis. Unless you live under a rock, you likely end up talking to another living person at some point during your day. It doesn't matter whether it's on a telephone, through Skype, or in person. What matters is that you're talking: you're having a dialogue. Once you've realized that, the writer in you can start to pick up on the little nuances of other people's speech and conversational mannerisms. Does the other person you're speaking with talk in a halting, deliberate fashion (i.e. Christopher Walken)? More importantly, do you understand your own manner of speech?
That last question caught me by surprise when I started asking it myself about three and a half years ago. I was preparing an appellate brief for a criminal case and was reading over the trial transcript. At the time, I still recalled what I said in the courtroom very vividly. Yet, when I reviewed the record of my direct, cross-examination and closing argument I noticed that there were little differences between what I recalled and what was written down. Every time I said the word "going," the court reporter had typed "gonna." Aside from making me think that I sound like I'm slurring my words, which I don't, this led to me understand that what the participant in the conversation hears (or doesn't) is just as important as what's said. Basically, this means that you have to ensure that this is a two way conversation, warts and all. Maybe one off the participants isn't really listening and gets the wrong information. Maybe the speaker isn't really paying attention to what he's saying and goes off on some ridiculous tangent. Maybe one of your characters does have a speech problem.
The point I make, is that we get to practice dialogue everyday. Paying attention to the conversations we have, and the ones going on around us, seems like one of the best approaches for honing that aspect of writing.