The temperature's getting cooler and it will be perfect to tennis! If your tennis string is old, dry and your arm hurts after playing...it's time to restring your racquet. Have a professional stringer string your racquet to ensure quality and consistent stringing.
There are many different types of strings in the market and a professional will be able to recommend strings that right for your game, depending on your budget.
Visit your local tennis shop and ask questions. They'll be glad to help. You will notice immediately an improvement in your game. Have fun!