What does your character have to lose/gain from your tale? Is the stake high enough? How does your character cope with crises? Do they bring out the best or the worst? Are there enough crises in your story? After all something’s got to happen!
Can you make use of your character’s memories to shape them? For instance, the Queen’s mother was murdered, obviously having a traumatic effect on the Queen and triggering her wish to keep her family close to her, no matter what it takes.
Do your characters have friends? What do they think of the characters? Could friends be useful for subplots (though note these still have to move your tale along and shouldn’t be a distraction or a device to get your word count up)? Can the friends guide your characters as to which route they should take? And friends can get it wrong, just as much as the main characters can by themselves.
Do your characters have depth to them? Do they fall in love, hold grudges, take revenge? Do they develop say from wanting revenge to finding revenge wasn’t as satisfactory as they thought it might be? Can you see why your characters act the way they do?
Do you show why your characters are villainous? Is the reason good enough to keep the villainy going or can it be overcome? Do you show how your world works? What’s the system of government? Are there those who resent the way things are run?
Can you picture your characters? I don’t have character biographies, though I can see the point of drawing them up, but I can picture the type of being that L’Evallier is in my mind’s eye and it makes writing for him, just to name one example, a lot easier.