Character voice isn't something I write in a first draft. While I certainly try to give the characters as much of their own personality as possible, I don't feel as if I really know them until after I've finished. Over the course of the book, they develop their own speech patterns and word choices, they use different expressions, but it's spotty. I still have to edit so that I can make it all consistent.
But I don't think "voice" rests just in dialogue, and I think that the details of characterization and those of speech should work together, creating an overall feel to the character. When a reader reacts to a character's voice they're usually talking about the overall experience of the character. If these two elements are in tune with one another, they reinforces that character. When they're out of sync and conflict with one another, a character may not have a clear overall impression. Which, sometimes, could be the point.
Once I finish the first draft and have a firm grasp of the character and their motivations, I go back and edit for characterization. First I work on any section in which they have a POV, and start working in hints at their motivations, and any factors from their past which might influence those motivations. I start with the POV sections because they're the places where the character can express motivations most clearly and it gives me an overview of when, how, and why those motivations change.
While the changes may take place outside their POV, I'm able to pinpoint the changes and figure out exactly how I want to show that transition. Even if I can't show that change from the character's own POV, I can hint at the reasons there, and elaborate on them when the character's next POV rolls around.
Next, I work on the POVs of the characters who know them best. I work in the signs that those characters can see in them, so they're more subtle clues, but if I need to make something particularly clear maybe the POV character will make an observation about the character I'm working on.
Most of the time, only the subtlest hints go in any other POV. Sometimes nothing more than the observation of a shared glance, or a half-noticed wince.
I like to deal with multiple POVs, I like the idea of showing all the different characters and trying to reveal something about them, even the bad guys. So it takes time to layer all that in. I sometimes get frustrated because it doesn't all come at once, but that's the good thing about multiple drafts and readers! You have time and crit to help you add all of that stuff in.
How do you add character to your characters? Do you find you have to go back an add it in or do you find they start speaking for themselves even in the first draft?
And, completely off topic, sorry about the craziness with the posts. Blogger ate the last post (10 Must Read Blogs and Sites) during it's outage, and then I re-posted it and then Blogger brought it back. So Facebook and Twitter got a little spammed because the post came up so often. So, sorry! :-D