Stuck for an idea?
Stuck for a plot thread?
Get up, get out of the house, and go somewhere. Drive, walk, bike, skate -- it doesn't matter. Give your brain a break. Take in some fresh air.
However, don't use this time to pay bills, hit the market, or go shopping. You don't need to be thinking. You need to open yourself up to whatever you come across, even if it's just a walk around the block.
You might be surprised at the results. :)