If I could prescribe you one activity to improve the rest of your life, it would be smiling. Smiling requires commitment, however, and sometimes that’s hard to live up to. When you decide to look at someone as they pass by and smile, you can’t hesitate or hedge on your bet that they’ll smile back. It doesn’t matter whether or not they smile back. It’s unimportant whether or not they’re having a good day before this moment. Your sole job is to smile sincerely and hope that, in some way, you can transfer your happiness to them.