Stringing a tennis racquet properly will increase a player's feel for the ball and ultimately the player's performance. To lock in the tension of the strings, a pro knot is used.
How to Tie Knots for Tennis Racquets
Secure your racquet on the stringing stand by clamping it on the side of the frames near the middle.
Main strings go up and down on the racquet, with crosses weaved through main strings horizontally. Starting with the inside top left half of your racquet, run the main strings half through the entire left side, finishing at the outer bottom left. Don't worry about tension right now.
At the end of the left half of the racquet, you will bring the string through the last grommet (protected hole) on the bottom left and across to the third line of main strings, pulling a second line of string through the grommet. The knot will be tied here with the extra string pulled through.
With the extra string on the right side of the main string, loop it over the main string. With the same string, circle under the main string. Keep the knot loose.
Bring the extra string over the last loop on the right side, and again pull it across and over the main string once.
Pull the extra string under the main string and through the first loose loop. The knot is tied and now needs to be tightened to secure the tension you will add by the stringing stand. Holding the extra string from the end of the knot with the pliers, pull the string tightly to the right. The knot should tighten against the frame of the racquet.
Further tighten the knot by then pulling across the base of the racket toward the left with as much tension as possible. Clip along the excess string, flush with the base.