You’ve probably heard this before but I’ll say it again:
The way to a character’s heart (and isn’t that where we, as writers, are trying to get?) is through the things he or she wants/needs/desires and the things he or she fears. The acts that the character does in order to get what he or she wants and to avoid what he or she fears create character. These acts in the main characters also often drive the story.
Kind of a big deal, really.
Thinking about this in early drafts might help you decide what happens next or how a scene should work. Thinking about this in later drafts might help you select what should stay and what should go.