I especially like the double wrist motion to activate the camera whether the phone is on or off. (itwire.com)
And I usually throw these out, though I think very often it takes ten of those over-labored efforts to produce one really beautiful wrist motion that is synchronized with your head and heart, and you have it, and therefore it looks as if it were born in a minute. (widewalls.ch)
You can use dumbbells, barbells, cables or any other tool that can add resistance to certain wrist motions. (all-about-arm-exercises.com)