Identify a character in your idea.
1) What does that character WANT?
2) What does that character need to do to GET what they want?
3) What are they prepared to DO to get what they want?
He gives a couple of examples (Superman and Hannibal Lector) and concludes with:
It’s a really simple way to discover a rough one-two-three structure that you can start to build on. You build on it by asking yourself what you can do to make 2) as difficult as possible for the characters.
So, figure out what a character in your idea wants, and then be an asshole to them. Voila! :-)
Read the complete post to get the full effect. Even if you haven't read any of his stuff (why not?), you should know that he produces a metric ass-load of content every damn day, so this is clearly a Good Idea.