I'm in the middle of reading The Writer's Digest Handbook of Novel Writing and I came across this article by Mary Kittredge called "Hot to Plot! A Plotting 'System' That Works." Kittredge's ideas seem simple at one level, but on another they seem bang on. For creating plots that work, she suggests the following system:

1. Start with your idea
   (her example is an attic that drips blood).
2. Create a character
   (in Kittredge's case, an innocent housewife who's been recently widowed).
3. Give the character a need or want
   (the police think she did it, so she wants to avoid suspicion).
4. Give the character a strong point
   (an intense love of nature)
   
5. Give the character a fatal flaw
   (fear of authority)
6. Now, put the character in a fairly stable situation and introduce the story problem
   (hmm, a murder suspect with blood dripping from her ceiling--done)
7. Have the character try to solve the problem, but end up making things worse by exploiting the character's fatal flaw
   (she's scared, so she calls a friend for help, but the police find out and arrive to investigate)
8. Repeat step seven as many times as needed
   (the cops come to her house and ask to come in--she says yes[out of fear] and they find her husband's body in the attic)
   
9. Make things look just as truly awful as you can
   (the cops are about to arrest her for the murder)
10. Develop an event that grows out ofthe character's strong point and shows the character her own fatal flaw
    (she sees birds eating out of a feeder in her yard, but one of the cops scares them away by looking at them--she understands that the cop is not a real threat to the birds, but because they're scared, they won't eat, and if they won't eat, they'll die--hence, their fear will kill them--she then realizes that her fear is just like the birds)
11. Demonstrate the character's strong point to escape
    (the body just happens to be in the only warm spot in the attic--everywhere else, the body would have frozen--she tells the cops why would she put the body in the only place that would get her caught?--the cops realize that someone else put the body there)
12. Wrap it Up
    (say, the character says, wouldn't the friend who I called for help also gain financially from my husband's death--and since I called her and the police found it, maybe she's trying to frame me--she tells the cops, who aren't stupid and realize that this is the truth)