Blisters form when the skin is exposed to prolong irritation through pressure or chafing. For tennis players, the racket handle is a common cause of blisters because they rub on the hands and fingers, which causes chafing. A typical match will involve hundreds of shots, and even a small rotation of the racket in your hand can cause blisters.
Choose the correct grip size when selecting a tennis racket. Grip sizes are measured from the middle of your palm, up to the tip of your ring finger. This distance, in inches, is equal to your correct grip size. If you are between grip sizes, choose the smaller, which you can adjust to make larger through the use of overgrips.
Use a fresh overgrip every time you play. As you play, a grip's tackiness deteriorates, making it harder to hold onto the racket and encouraging slipping. Slipping causes friction and eventually blisters. An overgrip is put on over your normal tennis grip to provide a disposable, tacky grip.
Dry your grip and hands with a towel between games and sets. A wet grip is harder to hold onto, encouraging slipping and friction.
Wear a sweat band on your forearm to prevent sweat from dripping down your arm and onto your hand during play.
Place a cushioned bandage on areas that start to become irritated.