It’s easy, and it really does affect the people around you.
Science has shown that our physiology affects our attitude. What does that mean? It means that it’s harder to be sad when you’re smiling, because the physical act affects your emotions.
Furthermore, we have what are called “mirror neurons” in our brains that are used to understand other people. This is why we go so far as to think that inanimate objects are behaving a certain way. This is called “Anthropomorphism.”
The mirror neurons mean that, when I see you smile, my brain fires in a way that is similar to if I smiled myself. This is why smiling, among other things, is contagious!
If I could go through life with the people around me smiling all/most of the time, that sounds pretty great. If this sounds good to you too, then lead by example and influence everyone else to smile more!