There are many types of "voice" in writing. The type of voice I'm talking about today is speech. How do your characters speak? Do they all sound like carbon copies of each other or do they all sound unique?
Even when I'm just starting out with a book and I'm still figuring out who the characters really are, I always hear them in my head. The way they would say something, the way they wouldn't say something. Everyone has a different voice. Different accents, different phrases, some very blunt, some very quiet. I have some characters who speak very formally due to background and upbringing. I have some characters who are more crass. The things that characters say can be as important as the way in which they say them.
As with characters' personalities, different things influence their speech: who they hang around, what they hear, what they read, what they do, what their personalities are.
Let's say I have some characters who all want to tell me they found my missing cat. They might all have very different ways of saying it. If I read someone talking, I might be able to figure out who is speaking just because of the way they say it.
Character 1: "I found your mangy old cat."
Character 2: "Hey, sweetheart, I think this is your cat."
Character 3: "I do believe I have found your animal."
Character 4: "Hello, Mrs. J. Were you aware that a domestic cat can run at speeds of thirty miles per hour? Your feline was very difficult to catch."
Character 5: "Is this yours? This stupid thing was hanging around in my barn! It scratched me! You're going to pay for this!"
Character 6: "Is this your kitty? She's so cute! Can I play with her? Can I come and visit her sometimes? Can I bring her a treat?"
The way a character talks says a lot about them. Do you "hear" your characters when you're writing them? Do they all sound different to you or are you unsure about how they speak?
One way that might help if you're having trouble finding a voice is to do what I did in the above example: pick a scenario and figure out how each of your characters would approach talking about the same subject. Writing their actions might help, too. Maybe one character is so shy that she just hands over the kitty and runs away without saying anything.
Do any of you have certain writing exercises that help you if you're having trouble with character voice?