|Does he like liver?|
How about him? Does he have a fondness for liver? Put in a few surprises, like his great grandmother dressed as a boy and rode for the pony express. Or she was a sharpshooter with a circus--which accounts for his being a sniper--something that fits.
One way to get to know your characters is to write a first-person essay about the life of each of the major characters, relating important or life-altering events for each one—kind of "My Life So Far." Give them some weird ability or quirk. Of course, these things need to tie in with the story somehow. Find the things that helped to shape his/her personality, formed her character. It may take a few days, but it's worth doing. This method really helps some people get to know their characters, and it will help you find the voice for each one. Each writer has to find his or her own way. Try it and see if it works for you.
Give both the protagonist and the antagonist a background and a personality. Say the heroine has trusted the wrong man more than once. The author should know why she falls for them. Are they much older than she is? Is she looking for a father?
If you cover the character’s life, you'll have much more information than you'll use in the story, but once you know your characters well, bits may find their way into your book. They'll make the characters richer and more interesting. How do you do it? What kind of things do you want to know about your characters? Are they your friends? Do you miss them when the book is finished? I do. I cry over them, laugh with them, believe in them. If not, I can't write them.