Characters swim into my psyche mostly intact. And since ye olde subconscious is holding the net, there's all kinds of Zoe-bits in each one - the flotsam, jetsam and half-chewed fish from the Wreck of the Edmund Fitzgerald of my brain - which means I now gotta work to make sure they're, yanno, them and not me. And one of the ways I do this is by probing as deep into dey biznass as I can
chiefly by being an ass to them.
Easy way to get another angle on your character? Take the scene you've already got in mind, then run it aground. Got her arguing in a diner? Drop her on a ship's haunted prow while some fucked up apparition screeches toward her - and her only escape is the black churn of water. What does she do?
Is he in a school cafeteria breaking up with his girl? Drop that motherfucker into the funeral of his ex's mother. What does he say? Female detective chasing dude through a Noo Yawk street? Plant her in Afghanistan, bleeding from friendly fire. What happens now?
Remember, you ain't gotta USE any of your alternate scenarios or even write 'em down. Imagining is plenty. Just like we grow best outside of our comfort zones, our characters develop more fully when you take THEM out of YOUR comfort zone (i.e., your planned scene), just to see what happens.
So, yanno, it's cool that my brain comes pre-populated with characters. It's cool if they snatch bits of my personality as they scramble out of my gray matter. It's not cool if they all look, eat, curse and otherwise act like me. That's how I separate church and state, anyway: First realize they're Bits o Z, then swap their situations to see how they act which helps make each one unique, whether they be sons, daughters, captains, cooks - or the North Wind or the Witch of November :)