This is part of a much longer article by Laura Miller - http://www.salon.com/books/laura_miller/2010/02/23/readers_advice_to_writers/index.html
and well worth a read:
1. Make your main character want something. Writers tend to be introverted observers who equate reflection with insight and depth, yet a fictional character who does nothing but witness and contemplate is at best annoying and at worst, dull. There's a reason why Nick Carraway is the narrator of "The Great Gatsby" while Gatsby himself is the protagonist. Desire is the engine that drives both life and narrative.
2. Make your main character do something. For the reasons stated above, many writers gravitate toward characters to whom things happen, as opposed to characters who cause things to happen. It's not impossible to write a compelling novel or story in which the main character is entirely the victim of circumstances and events, but it's really, really hard, and chances are that readers will still find the character irritatingly passive. When you hear someone complain that "nothing happens" in a work of fiction, it's often because the central character doesn't drive the action.
3. The components of a novel that readers care about most are, in order: story, characters, theme, atmosphere/setting. Of course all these elements are interlinked, and in the best fiction they all contribute to and enhance each other. But if you were to eliminate these elements, starting at the end of the list and moving toward the beginning, you could still end up with a novel that lots of people wanted to read; the average mass-market thriller is nothing but story. If you sacrifice these elements starting from the beginning of the list, you will instead wind up with a sliver of arty experimentation that, if you're very, very good, a handful of other people might someday read and admire. There's honor in that, but it's daft to write something with the deliberate intention of denying readers what they love and want and then to be heartbroken when they aren't interested. If you want to engage with more than a tiny coterie, take storytelling seriously; if you think that's incompatible with art, you are in the wrong line of work.