Hold a door open for someone at the bank, give someone directions if they look lost or make a point to compliment three people on your way to work. Small or big, directed at friends or strangers, random acts of kindness make the person performing the kind act happier when they're grouped together, according to Sonja Lyubomirsky, an experimental psychologist at UC Riverside. Doing a considerate thing for another person five times in one day made the doer happier than if they had spread out those five acts over one week. Lyubomirsky explains that because we all perform acts of kindness naturally, it seems to please us more when we're more conscious of it. There are social rewards, too, when people respond positively.