Squeeze the hand, hold it for a few seconds, then let it go slowly. The letting go is where the calm is, and it works better once you have practised the long version.

What the research says

In a randomised experiment comparing brief mindful breathing, progressive muscle relaxation and loving kindness practice, the breathing exercise did most for helping people stand back from their thoughts and react less to repetitive ones. So if what you need is distance from your own thinking, breath may serve you better. For the physical side, tension and release is still a straightforward way to feel the difference between held and let go.

Strength of evidence: one line of research. A single study, or a theoretical account.