There's been a great deal of research demonstrating that smiling offers significant benefits to our mental and physical health.
Zen master, Thich Nhat Hanh suggests a smiling meditation that I've found to be extremely useful. It goes like this:
"Breathing in, I calm my body. Breathing out, I smile.
Dwelling in the present moment
I know this is a wonderful moment."
It's important of course that you smile and hold that smile for a few moments as you recite the above. You may also want to try the inner smile meditation
Following is a link to an article that addresses the benefits of smiling as well as a three minute youtube video that deals with smiling.
Stay Healthy. Live Longer. Stay Married. Smile.