This is one of my favorite practices. If you're feeling stressed, worried, sad, out of sorts, just loosely hold a finger with the other hand. The acronym to remember this practice is:
Get rid of Worry FAST.
Loosely hold the thumb with the other hand if you feel worried.
Hold the index finger if you feel afraid.
Hold the middle finger if you're angry.
Hold the ring finger if you are sad.
Hold the pinky finger if you have a tendency to over-effort.
And if you can't decide what emotion you are feeling or don't remember which finger is for what, just hold the thumb - it takes care of everything.