When you find yourself ruminating and tell yourself "STOP" what are you going to think about? Sometimes you need specific direction. Having a list of pleasant thoughts can help you move from the rumination to thinking about something else. You might list things like an upcoming vacation, spending the weekend with friends, going out to dinner with your partner. Make sure your list includes situations you are looking forward to or pleasant memories. When ruminating, it is hard to "change the subject" and using a list gives you specific topics to think about.