Ann Crispin (famous sci/fi author) said in a workshop that when she cannot figure out what to write, she scrubs her bathroom floors. Sometimes it takes two bathrooms, and sometimes she gets all the way to the kitchen.
I get ideas while walking. Things start to fit together when I have the pulse raised, but do not have anything to concentrate on. The shower is another place where I am stuck for a while without anything else to think about. Sometimes ideas strike me there.
Now and then I have to work out big plot things, like who knows what and when do they know it, and why would they do the thing to get them from A to B. Sometimes I just envision the next part of the story.
Today, for instance, while walking I was thinking about the next part of a scene. The husband is driving home. He sees this spooky guy who has taken an unhealthy interest in the husband's wife. The spooky guy is walking on a lawn in his neighborhood, the opposite way of the husband's house, as if he is coming from that way--and there is no reason for the guy to be in this neighborhood, except to visit the wife, who is home alone. The spooky guy, oblivious, walks behind a house. The husband pulls up in the driveway and runs around the house, but does not see the guy. He looks for places the guy could have gone. Did he duck into the sun room of the house?
As I was out walking I decided that the husband should whip out his cell phone and call home. But there is no answer. The guy is somewhere close by. But there is no answer at home, so he's got to speed home at once.
Maybe that sounds like a little thing. I think it adds to the atmosphere and builds suspense. I will make some headway on the story tonight, then walk to work tomorrow.
I will be done with the story by the end of the month if my shoes hold out.