Run the motor at FULL throttle. Whether mowing or mulching, always run the mower at full throttle.
Do not mow wet grass.
If the grass is over 1-1/2" high, tracks in the lawn may result.
Be certain to clean underneath the deck after each mowing.
Ensure the blade is a mulching blade and it is installed correctly. If it is upside down, it will drop the grass rather than mulching it.
If the recommendations above are being followed and tracks still result, the engine RPM may not be set high enough. You may want to take the mower to an authorized service dealer to have him check the engine RPM.