Make sure a handle allows you to use it with your arm in the thumb up, neutral position. This reduces strain on your wrist and joints and enhances arm strength. Wood-handled tools can be easily extended or shortened in length or adjusted as described under hand tools to provide a spongy comfortable grip. What you wear in the garden counts, but fashion doesn't. If you do garden on the ground use kneepads or a foam kneeling pad.
Some gardeners wear gloves with nonslip, sticky grips on the palms to improve their grasp.
You may also attach hand tools to the wrist and forearms with splints or with long strips of Velcro-type material. If you have trouble getting up and down, a kneeling bench is a useful device. Some models of kneelers may also be turned over and used as benches. Another handy item is a garden scooter, basically a seat with wheels, which allows you to sit while you weed or plant. Wearing an apron or smock with large front pockets or a tool belt is a good way to keep garden tools, seeds and supplies within easy reach.