As a writer you should know your characters so well that if someone asked you a question about them, you would not show yourself up by not knowing the answer, or having to think about it for a few moments first. It doesn’t matter if you don’t use all the knowledge you have on the characters, but it does make them more rounded in your own mind, which brings them to life on the page.
There’s nothing better than when an interested person asks questions. Who is the MC? What are they like? Did he/she have a disturbed childhood? Why did they commit the murder, run away from home, become a witch? The more questions asked, the more you learn.
However, most of us don’t have an interested person to ask us questions, so we have to do it ourselves. Yet we don’t always ask ourselves the right questions, so the character doesn’t grow to their real potential. This is a shame, but quite normal.
Here’s a list of questions to get you started. I love to ask myself “what if”. It’s a great way of twisting a simple idea into something mad and exciting. What’s your favourite question?