Smile at older people, because they need to be noticed more often. Instead of using a cliche to lessen our generation, maybe they'll start to see us as good people.
Smile at small children, because they need the impression that the world is full of good, happy people. Let's make their world better.
Smile at everyone in-between, because life is hard. We all could use more positive energy around us.
Smile to yourself for whatever reason you can find within you, big or small. Even if you need to fake it for a few moments, it will help your brain produce more positive thought patterns.
Try smiling, it will change your world.