Our characters are the life blood of our writing. Whether you're writing fiction or nonfiction, it is the characters that will propel the reader through to the end. The last thing we want is homogenized characters that are reflections of ourselves. The best way to keep that from happening is to allow yourself to explore diverse personalities.
1) Find a subculture to drop yourself into.
The other night I went to a death metal show at Studio Seven in Seattle. Wow, was I out of my element but talk about fodder for unique character traits and images. I really believe it's healthy for us to be open and experience new and different perspectives. Am I going to gauge my ears and tattoo my chest? No. Do I now love and listen to screaming vocals and hard scratchy guitar.? Hardly. What I do have are great sensory detail and visuals that can come into play in my fiction.
2) Get in touch with your dark side.
We all have one, even if we have to dig pretty deep to find it. Have you ever been jealous, angry or manipulative? Everyone has at some level. When you've gone to the trouble of creating an awesome protagonist, don't weaken him with a lame antagonist. There needs to be a real fear that your hero could fail. You have to be able to understand and get inside the head of your antagonist. Don't be afraid to explore that side of yourself.
How do you get into character?