Each time you laugh, your breath deepens. But even if you aren't in a position to laugh hysterically — such as when you are interviewing for a promotion or taking your marriage vows — a good, deep, joyful breath is the next best thing. Diaphragmatic breathing . . . is the first building block of humor, because it turns on the body's relaxation system and cools down the limbic system. But deep breathing is only the first part of priming yourself for laughter. Now is the time to transform your breath into a smile.
1. Again, let your breath flow naturally into your diaphragm. As you do this, let your entire face relax.
2. As you continue to breathe, imagine yourself as the Mona Lisa, with the corners of your mouth rising slightly. Imagine your eyes lighting up with happiness, and feel the area around your eyes glowing and raising slightly. Let your smile begin to grow, and as you do, feel a tingle of lightness and happiness in your cheeks. You may sense a tickle in your stomach, a feeling that is connected to your smile.
3. Now, let the full radiance of your smile shine outward. Let yourself relax like this, enjoying the feeling of contentment that comes from resting in a joyous smile-just smiling for the fun of it. There's no need to have a reason. Even if your smile feels forced or artificial at first, allow yourself to smile fully and completely.
4. If it helps, imagine yourself in the presence of someone who always makes you laugh — even when you don't feel like it. Trust that your body will take over after you start smiling.
— Donald Altman in The Joy Compass: 8 Ways to Find Lasting Happiness, Gratitude & Optimism in the Present Moment