My wife and I have gotten into the habit of asking each other at dinner what was the best thing that happened to each other that day. She now likes this tradition so much she's expanded it into three things, which I contend makes the whole thing more of a mental exercise, but I usually manage. I have found though that it makes me take closer note of the good things that happen during the day, so I'm not left with "uh...." when it's my turn. It also helps punctuate the positive at a time when there's a whole lot of the opposite.