When choosing a tennis racquet, the first thing you should look is the grip size. Picking up the wrong one will lead to blisters. The grip size can be determined from the centre of your palm towards the tip of your ring finger. You can measure its inches using a tape measure or any other scale. This is the perfect grip size for you and you should note it before selecting the racquet. In case your grip size lies between then you can always get a smaller grip size racquet and extend with the help from overgrips.
Apply new overgrips when you play
You can use new overgrips each time you play a tennis match. Overgrips are grips which are applied over the original grip of the racquet. New overgrips will prevent blisters on your hand as when you play tennis, the firmness of holding grip lowers and eventually results in slipping. This slipping leads to friction and eventually causes blisters.
Use towel in order to dry your hands and grips after every game. This will wipe out the sweat and reduce slipping and friction from your hands. Remember that a wet grip is difficult to hold the racquet handle.
You can always wear sweat bands in order to lower chances of blisters. Wear the sweat bands on your arms which will prevent sweat from falling onto your hands during playing the game. It will avoid friction as you will have a strong grip over the racquet handle.
You can always apply cushioned bandage on the areas which are irritating you.
Toughen the skin
You can rub alcohol on your palm so that it toughens up. This will prevent blisters as it turns your skin hard.