Remember T. A. Barron? He was a guest 2 summers ago; he presented during a tornado and was lucky not to end up in Kansas. Among many wise things he said and many suggestions for writers, I still use something of his called (I call it that) The Interrogation Method.
His advice was to, among other things, note characters' deepest fears, hopes, longings and then ask, "What is your deepest secret?" He suggested doing this for every character, every place, and every magical/endowed object.
(It's fun to do it with less-than-magical-objects. I once asked a toaster just sitting there by the can opener while my characters argued. Its secret was an impulse to burn everything. No half-measures. No middle ground. It particularly hated "golden brown.")
I was reminded of Mr. Barron's exercise last week when I was fooling around with a couple of ancillary characters. Not even sidekicks. You know the guys who hold the spears in Shakespeare plays? Like that. Barely speaking parts. "No, m'lord." That kind of thing.
So on a whim I asked these accessories their deepest secrets. Holy crap. It was like sitting down next some some wan dude at a boring party and all of a sudden your ears are burning and you're half fascinated, half repelled.
I never felt the same about them after that. One of them disappeared from the story but the other one turned up toward the end and I thought, "I remember you, man. Did you ever get to see CocoRosie in person?"
Give it a try, especially if you're floundering. Stop paying attention to the stars of your stories. See what's up with the understudies. They'll usually spill the beans right off, but if they don't, twist their little, imaginary arms.