Just in case you don't have enough reasons to smile, here are five reasons I smile.
1. People look more attractive when they smile.
Seriously. I look better when I look happy, even on my worst day.
2. Generally you will have a better outlook on life.
I tend to be less of a pessimist when I smile and say "This is going to be a good day."
3. You'll be less stressed.
I am a high stress person, but when I smile I feel like it's going to be ok.
4. You will look more approachable.
Most people (not all) enjoy it when you smile at them. It helps people feel like you are a person they want to get to know or be around.
5. Physically you will feel better.
Sometimes when I feel sick, all it takes is a smile and saying "It's not that bad; you're fine." and I end up feeling a least a little bit better.