Eliezer Yudkowsky of OB suggests thinking and doing entirely new things for a day:
Don’t read any book you’ve read before. Don’t read any author you’ve read before. Don’t visit any website you’ve visited before. Don’t play any game you’ve played before. Don’t listen to familiar music that you already know you’ll like. If you go on a walk, walk along a new path even if you have to drive to a different part of the city for your walk. Don’t go to any restaurant you’ve been to before, order a dish that you haven’t had before. Talk to new people (even if you have to find them in an IRC channel) about something you don’t spend much time discussing.And most of all, if you become aware of yourself musing on any thought you’ve thunk before, then muse on something else. Rehearse no old grievances, replay no old fantasies.