I have a hard time making my characters different from each other. I've tried filling out the character questionarre sheet, and when I'm done, they all look similar. Do you have any tricks to making each character stand out in his or her own way?
How do you create you characters?
However, I've found that my characters only come to life for real in the course of writing their story. So right now, I'm okay with starting with sketchy characters - I can always go back later, when I've learned who they are and what they are like, and fix/write in whatever I need to complete their portrayal consistently throughout the story.
And that's that, really - when I started my current WiP, I had very vague ideas as to who the characters were - three chapters later I had a new main character, who seemed nothing special at the beginning, but ended up evolving so much that I realized it was, in fact, his story.
Their actions in the story define their personalities for me. They are created as they're written.