Try to make at least three people smile each day.
Okay well this is the fun one. I love to smile at people; and sometimes the reactions you get are interesting. Some people frown even more, some even scowl. Those reactions just make me smile more. I think that if you are so miserable that a stranger smiling at you makes you worse or even angry then you really need more smiling, and besides that it is funny!
The reaction that is most often observed is a simple smile back. Some of the smiles look uncomfortable. That leads me to believe that as humans we are not being friendly enough to each other. I get to see hundreds of children 5 days a week, and that in itself is wonderful, but let me tell you that they are most receptive to smiling. You can almost guarantee that when you smile at a child they will smile, and if you continue to smile back they might even giggle!
Next time someone smiles at you look back at them, smile, and say hi.