Goals.  Or more precisely, your characters' goals.  They're like a suitcase for writers, a place where they can store all sorts of great things.  Things like conflict...emotion....back story.  Goals can be obvious, like those of an professor/archaeologist who travels the world saving historic artifacts from the Nazis.  Goals can also lurk below the surface of the story.  Consider the young Star Fleet officer who is driven to prove the Academy wrong and best his own father's sterling record.  Gee, can you tell I like movies? 

Goals not only drive your characters, they hook your readers.  Like conflict (discussed previously and coming again soon to a blog near you), they have the power to keep the reader hanging around.  They're curious to see if your character achieves their goal(s).  Does he overcome the Dark Lord?  Does she make it out of the killing arena alive?  The best page turners have goals galore.  For some great insight into this subject, check out author Robert Gregory Browne (www.robertgregorybrowne.com) and his take on identifying the goals of your characters.