Learn to pay attention to your strings.
They are your most important piece of equipment.
Remember, the strings are the only part of the racquet to contact the ball. At least that is our goal! If your racquet is starting to feel dead; if you have to swing harder to get the ball deep; if you are making good contact, but getting fewer solid hits; if your strings sound different when contact is made; or if it feels as though the sweetspot has disappeared, then it is probably time to restring.
Strings may feel tight, but play dead.
This is because strings lose their elasticity and resilience, which is their ability to return energy to the ball.
When strings wear out, the string stretches further, but rebounds slower with less force.
The strings return less energy to the ball, resulting in less power to the shot.
Strings don't have to break to be worn out (dead). How often you restring depends on your racquet, string type, style of play,and frequency of play.
A good rule of thumb is to restring as many times each year as you average playing each week.
If you average playing four times per week, you should restring every 3 months or 4 times per year.
As a minimum, you should restring every six months because strings will go dead in this time regardless of the frequency of play.