One of the most vital aspects of a novel that's often forgotten by rookie authors is the "so what?" or, in other words, the consequence. What happens if your main character fails in his quest? What if she doesn't break the curse? What if he joins the dark side? What if they don't reach the Emerald City? What is the consequence? What's at stake?
Part of thinking about your story in terms of consequences is thinking about the actions that precede the consequences. So basically: this action leads to this consequence, which leads to more action. Sometimes, consequences stem from your main character's decisions. Other times, the consequence is created by others' actions, which in turn affect the main character. Whatever the case, in a great story, something is always at stake.
Let's take The Hunger Games, by Suzanne Collins, as an example. Katniss Everdeen has one thing she loves completely: her little sister, Prim. When Effie Trinket draws Prim's name (action), Prim must fight to the death in the games (consequence). But Katniss cannot bear to watch her sister fight and inevitably die, so she volunteers to take Prim's place (action) and engages in a fight to the death (consequence).
What would have happened had the story been more like, "Prim sat at home, and one day she died. And Katniss cried." That's hardly a story. Even, "Prim's name was drawn, she fought in the games, and she died. Katniss cried." That's a little bit better, but still not a bestseller. But this, "Prim's name was called, Katniss cried out that she would take her place, and Katniss was immediately taken away from her family to go fight to the death in the games." Now that's a story people want to read. That's bestseller material.
So what is the one thing that matters most to your main character? Is it family? Honor? Love? Survival? Whatever it is, take it away. But remember that it needs to be a consequence of someone's actions. For Katniss, her family was at stake. And then her own life hung in the balance.
Now, it was her choice to volunteer to take her sister's place in the games; it was her actions that forced her to deal with the consequence. But whose actions forced her to make that decision? The Capitol. And that is how an antagonist is born. The actions the villain takes against the hero are a means of revealing the villain. (If you want to throw your readers off the trail of the antagonist, have him take actions that benefit the hero at first. Then later, reveal that his actions were all just to further his plot to destroy the hero in some way.)
Every character or group will take action in your story. Does Katniss volunteer? Does Peeta throw the bread? Does Haymitch send supplies? These actions will all lead to consequences and future actions. Imagine how things would be different if any of these characters (or your own characters) had made different decisions. The consequences would be different. If you are stuck in writer's block, look at the consequences of your characters' actions. Make the consequences more severe. Put something even more important on the line. Does the character have anything left to lose? If yes, then put that on the line. If no, then put her life on the line.
The most important thing to remember is that without any consequences, there's no story. If Prim's name was drawn to receive a sack of potatoes, then Katniss would pat Prim on the head and they would go home. And that would be it. Or would it? Even the most innocent of actions can have dire consequences if you, the author, make it so. What if the sack of potatoes had been poisoned? What if the rest of the town was starving and they end up breaking into Katniss's house just for the potatoes? What if both of those things happened and the members of the town began dying off because of the poison? And then comes the question: who poisoned the potatoes?
Though a story about poisoned potatoes may be interesting, a story about a girl who has to fight other teenagers to the death may be a bit more interesting. So don't be afraid to raise the stakes. It is only when the consequence is so terrible that the character feels like she has no choice. And it's when she feels like she has no choice that she makes a decision. Does she sit back? Or does she stand up? Is she ready to face the consequences of her decision? Well, ready or not, she will have to.
So, you're an author and you write a book with high stakes and drastic consequences (action). So what? Well, readers will stick around to see what happens (consequence), and maybe you'll be the next bestseller (even better consequence).