Creating characters is hard enough. Now at the end of your first draft you should know at least a hand full of facts about them including their name, physical characteristics, and the other everyday things. Right now for most of us and for most of our readers our characters are average. When we are revising, we have the chance to create unforgettable, one-of-a-kind fictional people. The best way to do this is to describe. Describe, describe, describe. Describe their room, their family, their house. It will help you give your character a whole other level of life. Plus, it will help your readers visualize their room and learn more about the character's personality and life style.
You have your own writing voice. Every writer does. Now try turning your voice in to your character's voice. The next time you are in a meeting or dinner instead of talking, listen. If you have pen and paper, you might want to jot down some notes. Listen to peoples voices, note their body language and appearance. After a couple times of doing this, you'll probably start to get a feel for how certain people talk or act a certain way. From there you can figure out what you want your characters to sound like on the page.