I find that every one of my characters has evolved a bit differently. I've had a couple spring full-grown from my head and only change once they hit the page and start acting and reacting within the story. Others, I've sat down ahead of time and filled out endless questionnaires and character sheets for, before finally finding the combination of traits that makes them feel right.
In general, I find that starting by figuring out who they were - before the beginning of the story and by whatever method you find works best for you - is the best way for me to develop a character. When I know who they've been and what they've done up to the start of the story, they tend to take shape more easily and naturally on the page. Developing a character that way also gives you all kinds of backstory for them to refer to in conversation, especially if they have shared history with another character.
Hope that helps a little.