Take a blank sheet of paper. Write one word in the middle, one that has to do with where you're blocked. Around it write whatever words come to mind while looking at the first word. Then around those, write whatever words brought to mind by the secondary words. Keep going, if necessary until the paper is full. It encourages "lateral" thinking; thinking in a different direction than you usually do. Somewhere in that mix of words I usually find something that will get me moving again.