Tip #203: Start with the antagonist

Conventional wisdom: The hero drives the story.
This is correct, but it's the end point of the plotting: it's what the audience see.  The antagonist is the part of the story that will cause all of the surprises in the story.  The more of the opponant that's hidden, the more plot you have: the more danger, the more surprises and reveals you can spring upon character and audience.

http://www.youtube.com/watch?v=n_mZ-XokOTg

Again, this tip has been paraphrased.