I will warn you right now, this is mostly a rant/stream of consciousness type thing. So, it's not well thought out. So if you read it, do so at your own risk.
I've been having this huge problem lately.
I've discovered, as I try to write my stories, that all my characters sound the same. The prince sounds like the mercenary sounds like the duchess sounds like the inventor sounds like the historian...ect.
I get that characters are supposed to sound different. They're supposed to be products of their environment and how they grew up and their education level.
Instead? They all sound like me.
Grand, ain't it? They all sound like middle-class, high school diploma, twenty something women from mid-America.
What am I supposed to do with that? I mean, honestly. How are my characters even supposed to sound? (About the only answer I got is 'not like me'. At least not usually.)
I've tried character personality sheets, but them things just seem to make it worse because they want to know things like 'do you characters sleep in the nude while away from home?' How is something like that even going to help with character building - much less voice?
I've tried thinking about what the characters want, but that really only helps with internal voice, not when they talk. (And I'm almost okay if the narration sound the same between characters so...)
I've heard it said that you shouldn't be able to read more than a couple sentences without tags before knowing who's talking. With my characters? You'd never be able to tell who's talking without tags. (Unless, maybe if they're talking to their oldest friend, and even then...probably not.)
So, I've been trying something for the past two months.
Have you even heard of visual novels? (If you haven't go look them up because I'm not explaining it.) I've been trying to write one. Just a short one, but so far it has helped me a little because so much of the characters and information is communicated through dialogue.
Which means I constantly have to stay on top of the differences in my characters. So far the differences are fairly simple - but it's also helped me out a lot.
One of the most important things I've learnt is that characters don't have to say the first thing that comes to your mind - and they certainly don't have to phrase it the first way I think of it.
Seems simple, but I think my writing just got a little better. :)