- The character makes decisions and affects the story.
- The character has his/her own motivations.
- The character is more active than reactive.
- The character pushes on the plot more than it pushes on the character.
- The plot exists as a direct result of the character's actions.
In short, characters need to be more than just victims, sex objects, or "action figures" that are posed to fit the situation.
As Wendig said in another post from last year (which I hadn't read before now), "Characters without agency tend to be like little paper boats bobbing down a river of your own making. They cannot steer. They cannot change the course of the river. The river is an external force that carries them along -- meaning, the plot sticks its hand up the character's cavernous bottom-hole and makes the character do things and say things in service to the plot. Because characters without agency are really just puppets."
I've written six (practice) novels now. You would think by this point that I've mastered this whole "characters drive the story" thing. You would also be wrong. As I look back on the novels I've written, I can see that failing to give my characters (male, female, or other) agency has been a big piece of the problem. I've got some others to fix, to be certain. This is a big one, though.