Smiling is a good way to improve your mental health without much effort. Not only that, you will also make other people happy.
Try it. It is really easy. Stretch your lips and curve them upwards. Go on. You can do it. A little bit more. You are nearly there! 
See how much better you are feeling already!
That’s so true! I try to smile everyday as it instantly lifts up my mood. I must admit, smiling is contageous, and I smile whenever someone I like smiles at me!