I've found that an interesting way to get deeper into my main character is to throw them into something outside my WIP. All it takes is one line -- a response in dialogue, a reaction to an event, a feeling about a moment. It's easy, it's fun, and it doesn't take much time.
I decided I'd like to share this with the rest of you. I'll post a quick prompt utterly outside my WIP, and my MC's quick response to it. I'd love to see some of your responses in the comments, but even if you don't feel comfortable sharing there, I hope it spurs some thought in your own writing process.
Your Main Character was approached by a stranger on the street, who asked, "Hey, got a light?"
A) Gambler #1 shakes his head silently, conscious of the cherry wood pipe in his pocket, and suddenly feeling a little silly for never having lit it.
B) The Detangler flicks the cigarette out of the stranger's hand and smirks. "No smoking in public."
How about your character?