Your first, best source for characters is your own personality.Writing For Comics & Graphic Novels with Peter David, page 46
When creating characters for your stories the greatest challenge is making them "real". Personality traits. Flaws. Character tics. Take your pick. But did you know you can add something really cool to your characters...Yourself.
Well, not all of yourself into them. Just bits and pieces. Your past to your experiences as a high school teacher. We writers invest aspects of ourselves to create identifiable characters in a manner of ways. For instance, Diana Rowland has poured in all her years in law enforcement for her Kara Gillian series, giving it the realism not all crime solving/urban fantasy books have. Comics icon Stan Lee would tell you about the "origin" of Spider-Man from his teenage years when he was, to a degree, a lonely kid desperate for acceptance.
The more honest you are about yourself, the more you can give readers something to identify with in terms of characterization.