I often speak to clients about the power of facial expressions affecting emotions. Consider this classic research by Strack and colleagues from 1988. Undergraduate students were instructed to read comic strips while holding a pen in three different positions: teeth only (smiling face), lips only (lips squeezed together in a pout), and non-dominant hand. Mean ratings of overall funniness were highest when participants held the pen between their teeth in the smiling position. Manipulations of facial expression (smiling) led to an improved affect state (higher ratings of funniness).
You can benefit from this research by adopting a half-smile, a small grin with the corners of the lips turned slightly up. This slight smile, often unnoticed by others, can lead you toward feeling more positive and accepting of yourself as well as those around you.