I am practicing, with success I may add, the art of the smile. My sister once passed on a trick: if it's all going pear-shaped or you are just a little lacklustre, practice smiling behind your hand (she told me it was a monks trick but don't quote me on that). Not only does it feel slightly ridiculous, it does make you feel better & then, subsequently, everyone around you. If you are glum, a smile is contagious & can make you happy or at least offer a slight upturn of the mouth.
So turn that frown upside down (even if you don't feel like it). I visited The Smile Cafe on Bond St with my lovely friend (& very clever stylist) Kim Ficaro, we had the best breakfast & catch up plus this place has the best food, philosophy, interior, book & packaging. This is a chart from the website to demonstrate the very large variety of smiles available to you.