What does the character want? This is important because it gives us something to care about and vicariously fight for through the protagonist, especially if we sympathize with them—see Question #1. This can even help us identify with an unsympathetic character because basic wants humanize people and help us feel connected to them.
For example, if a father desperately want to take care of his family, we can understand his motivation for doing illegal and immoral things to get money. (This blog series is about books, so I won't mention a certain very popular TV show that deals with this, but I bet you can guess!)
Remember that forming a connection between the reader and the character has "surival" purposes because a character who engages us also encourages us to want to keep reading and glean the important meaning from the story.
Wants can change over the course of the story, of course. They should change, to keep the story interesting. Make sure to start with a strong want from the very first page! It might not be the main "want" of the story but we need something to attach to and route for.
Think of want as something tangible and active, rather than deeper and more emotional. For example, finding a romantic partner, having a child, saving a house from foreclosure, overcoming an illness, rescuing a loved one, escaping a violent regime are all wants we can identify with and that have the potential to be built into an active storyline.
The more active the main character is, the better. I used to think that what made a character sympathetic was exposure to adversity, but I have learned that it is actually fighting in the face of adversity. We don't want to pity a character; we want to route for them. Again, this plays into the survival idea because an active character keeps us on the edge of our seat, turning the pages to find out what happens next.
In TO KILL A MOCKINGBIRD, Scout wants to go to school in the beginning of the book. But her greater want is to defend her family, even if it gets her into trouble. Both are active wants, rather than just things for her to ruminate about. Atticus wants to teach his children about the nature of good and evil.
What does your character want in the beginning of the book? How does it change? What other wants come up? Does your character pursue them actively?