Words with JAM - the ezine for writers - has created an exercise: a list of questions that you answer as one of your characters. It's a pretty detailed list, including questions such as what makes you easy/difficult to get along with, describe one of your rituals, what' the last thing you do before you go to sleep and are you normal.
Answering questions as one of your characters can really help you ensure that your character stays consistent throughout your book and can help you work out how describing a character's traits can help you move the plot along, or add in relevant detail.
You can try out the quiz at Words with Jam, here.