Getting to know your main characters can be a tricky business. If they're proving to be somewhat enigmatic, here are some questions (in no particular order) to ask yourself that may help.
10. Is their appearance important to them?
9. Are they happiest surrounded by people or by themselves?
8. What is their idea of a perfect day?
7. What is their first priority?
6. What are their strengths?
5. Who is the person they are closest to?
4. What is their greatest fault?
3. How well do they know themselves?
2. Do they believe people are naturally good?
1. What is their greatest fear?
There are, of course, many other questions you can ask. What questions do you use to help get under your characters' skins?