This might be on the "not-as-helpful" side as some of the other more concrete suggestions for character motivations posted, but here it is:
It's okay to throw some of this back on the player's plate. Try this response when asked, "So what would my near-to-being-a-God character want to do?"
You: "That's a great question! And I'm glad you're thinking that way about the game because Amber is ENTIRELY about finding your character's deep motivations and developing your own personal goals. Imagine that you, the player, have just been granted an immeasurable lifespan, granted the ability to learn any skill or trade you want, granted the ability to meet anyone you want, even people that you make up in your head, granted great strength, intuition, and health...what would YOU do? Try not to think about what would 'a' godlike being do, but instead what would 'YOU' do as a godlike being. You don't need to answer right now, cause it's a big question and there's lots of possibilities, just sit with that idea for a while and exercise your imagination and indulge your sense of, 'what if?' You'll probably happen across at least one or two things you might be interested in doing, and that'll be enough to get you started -- then you'll run into stuff I've planned for the game and we'll take it from there."
If you're lucky enough that the player comes back with THREE ideas, then you can say that the character has accomplished his first goal, is on the verge of accomplishing the second one, and has finally gotten all the pieces together to get the third one comfortably underway when the plot happens and gets in the way of his personal plans.