So, one of the things I’ve noticed lately in the books I read (must I use Cassandra Clare as a negative example again? Yes, I must) is the lack of distinction in character voice. Character A has the same mannerisms as Character B, Character B has the same voice as Character C, etcetera, etcetera, etcetera. So how do you make characters sound different?
1. The way they word things should be different. One character might say “You’ve gotta be joking!” while another might say “You aren’t serious.” Look at the differences: “You seem worried. Are you all right?” vs. “Hey, you okay?” or, “Do I look like I care?” vs. “I’m really not interested.” Once you get into the groove of the way your character talks, it becomes habitual to write them that way.
2. Everyone has different mannerisms. I have this weird tic where I rub my thumb and pinkie together. My sister jiggles her foot like there’s a scarab beetle in her leg. A tough guy might fold his arms across his chest all the time. Another character might slouch. Keep mannerisms consistent with the character.
3. Clothing is a big deal. Your bubbly manic pixie dream girl might wear pink and high heels, or she might surprise everyone and be popular in spite of the fact she wears 100% black. Just keep it consistent. (Consistency, consistency, consistency! There’s a pattern!)
4. Their voices should be different, and so should their thoughts. If we’re inside the characters’ head, then we should pay attention to make sure their thoughts sound the same as their speaking voice. It’s the same character, just a different way of expression.
5. Their sense of humor. One character might be completely sarcastic. Another might have a lively wit. One character might be slapstick. Another might like to crack jokes. Someone might be straight-laced, or tongue in cheek. Or they might have no sense of humor at all. Your choice.
Those are the main bases I try to cover when creating a cast of characters for each novel. Is there anything specific you do? Oh, also: If you aren’t used to creating characters like this, character biographies are really helpful. I used to use them all the time before the process became more natural, so I definitely suggest those.