I'm a big fan of smiling.  I think it might be one of the best things invented.  It's almost as contagious as yawning and much better than a great sneeze.  It's international and the best way to introduce yourself to a stranger who might go on to become a friend for life.  If you're proud of your teeth a big smile might result in a tooth modelling contract, and if you have no teeth then, well, show off those gums!  

Here are some happy smiley folk who've I've come into contact with over the years.  Try not to feel a little twitch in the corner of your mouth... I dare you!