Scrunch a piece of paper up into the smallest, tightest ball that you can. Use only the affected hand to do this. As your hand strength increases the ball will get smaller and tighter.
Repeat for the number of sets and reps indicated.
Start with two hands if scrunching with one hand is too difficult and progress to single handed as you get stronger.
Do not tense through your neck and jaw. Place the tongue on the roof of the mouth to activate the deep neck flexors and as a reminder to not clench through the jaw.