What do you do when your character is too resigned or weak? She may want things, but she doesn't want them enough. Readers don't want to read in the head of someone who does not want something. Wanting chocolate enough to complain about it doesn't count, unless the character is traveling to the world of the damned to trade her soul for the alchemist's ring, granting her the skill to turn anything she wants into chocolate. I know, that was terrible.
Another way to write a character who will drive the story is to discover what she wants through dialogue. Interview her and ask her questions about herself, her family, her friends, her greatest fear, and her greatest desires. What does she want more than anything else and what is she willing to do to get it?
Stein also suggests composing a letter--from the new character to the author. A letter that is candid, bold, and a touch eccentric. In the letter, the character should reveal to the author something the author doesn't already know. As odd as it sounds to write yourself a letter, as your character, it is a surprising and powerful writing exercise. One that may answer questions about your plot.
How do you flesh out the personalities and wants of your characters?