Imagine how wonderful our planet would be if each person on it would greet everyone with a smile. That means that wherever you go you would be met with a smile. Be part of the "Bring a smile to our planet" project. To become a member of this project, you don't need to spend any money or fill out any forms. All you need to do is smile. Then watch the faces of those at whom you smile. Reinforce the smiles of others by telling them, "I appreciate your smiles," or, "You look great when you smile." By reinforcing this person's smiling, you will set in motion a chain of smiles. The recipients of this person's smiles will smile to more people, and those people will smile to even more people. You will be increasing the total amount of smiles on our planet. And that's something we need a lot more of.
Think of someone who doesn't smile very often. Then sensitively think of a way to bring a smile to that person's face in a way that will be appreciated.
(From Rabbi Pliskin's "Happiness",p.167)