Handwriting relies heavily on shoulder, arm and hand strength, coordination and dexterity. Here is one, fun way to increase these skills, as well as visual tracking skills which are also necessary for reading.
You will need a pair of tongs, some small bean bags or bundled up pairs of socks, and a target which can be another person or a stationary target. The goal is to throw the bean bags or socks and hit the target, and then catch the bean bags or socks with the tongs. It's harder than it looks, even for adults!