First make sure all the tires have the correct pressure.
Then I always parked on a flat and level spot and measured from the mower blades to the floor. Turn the mower blade so it is closest to the left side and measure there, then turn the other outside blade to the deck opening and measure there. Once it is level from side to side, turn the blade pointing to the front and repeat to level it front to rear.
Then I always parked on a flat and level spot and measured from the mower blades to the floor. Turn the mower blade so it is closest to the left side and measure there, then turn the other outside blade to the deck opening and measure there. Once it is level from side to side, turn the blade pointing to the front and repeat to level it front to rear.