Literature comes alive when read out loud, and best if it's done with some panache, even if you're working alone. Characters make their impression based on what they say, what they do, and what others say about them.
Note these qualities and infuse your character's dialogue with them as you read.
Stand up. Physicalize the character traits. Smile if they are happy, smirk if they're nasty, turn up your nose if they're snobby, grit your teeth a little if they're angry. This will help bring the right color of emotion into your voice.
You'll be surprised at the insights and questions that come up. Note them. By living the story from within the characters this way, you'll start to more fully understand their motivations, making it easier to see what they stand for in the story and bring your knowledge into your writing.
This even works with history. Or math. That's right. The strange and complex beauty of the quadratic equation has character. Play around. Talk yourself through the steps of calculations adding a little emotion, or an accent. This can make it fun, helps with focus, and get you unstuck when you're bogged down.