[g.willikers]

Buy one of the afore mentioned soft foam or rubber balls.
I use one shaped like a little football, because it's shaped more like a pistol grip than a round one.
But either shape works.
Extend your arm, one hand at a time, like you would hold and aim a pistol, and squeeze and hold as long as you can.
Then repeat as much as you can.
This will strengthen hands, wrists and forearms, without harm.
Curling exercises with weights works, too, but using weights requires good instruction to avoid possible damage to wrists, elbows and shoulders.