i recommend reading a short story(books take too long), watching a movie, or listing to music.
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in all actuallity i suggest going into a city and watching the madness on the streets. Or perchance do something completly out of the ordinary. if you watch alot of "variable X" movies, books, games, music, then go and listen to "variable Y".
suggestions:
you watch action movies watch a drama(trainspotting, requim for a dream, etc..)
you listen to rock listen to smart rap (immortal technique, aesop rock, vakill)
you play lots of "simple/normal" games play some artsy ones(killer 7, ico, flower, okami)
you get the drift...different.
that usually helps me out.