"Strings are the soul of the racquet" and most often neglected. Your racquet starts to lose tension shortly after stringing and that is why it is recommended to re-string as many times per year as you play per week. If you play 3 times per week - you should string 3 times per year. It is also important to choose the correct string, tension, and gauge suitable to your game.
Replace broken or damaged grommets, and bumper guards, as well as worn out grips at the same time. Always keep your equipment in good shape to prevent injury and allow yourself to play your best tennis.