I've heard of writers who create a character then follow a basic method to get to the heart of their new creation - interview them. Imagine you're the interrogator and they're sitting right in front of you all smug-like (depending on the character of course). You ask them all sorts of questions a cop might ask a murder suspect.
This forces the character out of their comfort zone and makes them address the issues they'd rather avoid. (NB - I say address here as opposed to answer, because some characters might stay silent)
I've never used this method, but I can see it would be a brilliant way to strip the character bare and see who they really are. I don't recommend you do this in a cafe though - you'll look a wee bit weird! But if anyone's brave enough to record themselves doing this, I'd love to see it!
SPOILERS: 'SUPERNATURAL' SEASON 3
Anyway there's a scene in 'Supernatural' that reminds me of this technique. Dean (Jensen Ackles) essentially argues with himself. Something that makes Dean cool is the clothes he wears, the way he acts, the music he listens to etc. That's who he is. But if you (the writer) decided to tear those aspects apart, what would happen? Probably this......
Notice how Dean (the real Dean) is stripped naked? (Sorry female readers, not literally!) He goes from his usual smart-mouthed self, complete with cocky attitude to a quivering wreck when forced to address the things he'd rather avoid. What was once cool about Dean is revealed to be.......pathetic(?) - the awesome Chevy Impala, the music etc
This scene also gets down to the heart of Dean's character. His sole goal in life (and in the series) is to look out for his little brother Sam. The writers never lost sight of that throughout the show and this played out brilliantly as a result.
And finally, address one of the most important issues when it comes to characters - fear. Your characters have to be afraid of something. That's what gives them something to lose in their journey. Whether it's not winning the football match, not winning the fight, not saving that damsel in distress, or - in Dean's case - becoming a demon.
Strip your characters down and take them to a place they'd do anything to stay away from. Expose their dark side. Make them overflow with emotion. That might result in buckets of tears, a psychological breakdown, a suicide or a blast in the chest from a sawn-off shotgun. Just please remember to take the proper precautions when interrogating your more violent characters - always wear a bulletproof vest (just not this one)!
Expose their fears and see what happens. There's a saying that goes "You don't truly know someone until you fight them." It's true to a degree. But I'd say "You don't truly know someone until you take them to an emotional place." Only then do you really know what a person is capable of.
Try this next time you want to really get to know one of your characters!