(From Darths & Droids)

Roleplaying games are, in some sense, all about getting to make decisions in the game world that you never get to make in real life. Decisions that are really important. Decisions that can change the course of history.
The Playing Characters are the people driving the story. What they decide to do really matters to the people around them.
As a Game Master, it’s good if you can really underline this point at some stage during an adventure. Make them acutely aware of the import of what they are about to decide. Make it painfully clear that the lives of thousands, or millions, or even billions of people will be affected by this decision. And make it a really tough one. Back the characters into a corner against their morals (alignment is a handy tool here). Throw them on to the horns of a dilemma.
Put them between a rock and a hard place.
Scylla and Charybdis.
Make them sweat.
Make their own safety hang in the balance as well.
And then give them a time limit.

Yes, this is directed people participating in RPGs, but it makes sense for writing as well. Conflict drives the story and makes it interesting. Course, somehow you have to come up with the conflict, which can be rather difficult…
Thanks to Ash for pointing out Darths & Droids to me.