How do you develop your characters for a book?

What I do is develop a huge flaw in my character that drives them to make a mistake in my story, and thus drive the plot further. Because characters who are perfect don't face conflict, and what's a story without conflict? For example, I have a character that's a police officer who is too worried about catching every bad guy, and she becomes so OCD with catching them that she gets reckless and almost dies. Flaws = interesting characters, in my opinion.

I create them by starting with a personality for them.

What are they scarred of?

Are they shy or outgoing?

Do they have drop dead good looks?

What would there best friend be like?

But as I write the book the character just kind of creates itself as the story unfolds

all ok