1. Think about your character's interests and passions: The things your character cares about will shape how they see and describe the world. For example, an artist will use different words to describe a sunset than an athlete. An artist might describe the colors and beauty of the sunset. An athlete may take more notice of how the world around them darkens rather than the sunset itself, or maybe they notice the drop in temperature that sunset brings. In Unearthed Greg is a fan of horror movies, and in his chapters, he makes a number of references and comparisons to different horror movies. Caroline, however, is not a fan of scary movies so in her references and comparisons are more likely to be related to music.
2. Think about HOW your characters think: Does your character find themselves deep in thought often, or is there more brevity to their thoughts? Are they full of wonder, do they question things, or are they accepting of the world around them? In both Greg and Caroline's chapters, there are some beautiful descriptions, but Caroline's chapters are definitely flowier while Greg's are more to the point. Caroline notices more details than Greg does.
3. Consider your character's word choice: Does your character say soda or pop? Water fountain or bubbler? Do they refer to that piece of furniture in their living room as a couch or a sofa? Caroline is far more likely to be more specific and detailed in her descriptions. For example, if she points out the color of something she's more likely to say maroon or burgundy, where Greg is more likely to just say red. They also each have specific words they use that the other doesn't. When writing Unearthed I actually made a chart to remind me of their different phrases.
4. Edit your chapters out of order: If your chapters for each character alternate, do a read through where you read only character #1's chapters, then do a read through where you read only character #2's chapters. This can help you pay attention to their voice and character growth. With Unearthed, I would edit all of Caroline's chapters, skipping over Greg's, then go back and edit all of Greg's, skipping over Caroline's. This way I could focus on the voice of that character across the span of the book.
5. Take your character's gender into consideration: This is only really useful if the two characters you're alternating between are different genders, and it's important not to make your characters stereotypical. But, some gender stereotypes hold true and can help you form your characters. Maybe your female character shows more emotion. Maybe she's more social. Your male character might notice the physical attributes of your female character more than she notices his. Like I said, be careful of getting swept up in stereotypes, but remembering that men and women do sometimes see the world differently may help you differentiate your character's voices.
