Use the Left and Right Hands in Cooperation
Meyer's dagger section provides a number of precepts; general principles for dagger fighting.
The third precept tells us to use both of our hands while fighting with the dagger. If we're defending with our empty hand, then the dagger hand should be attacking. Or, as we defend with our free hand, the dagger hand should be moving to reinforce the parrying and make to grapple. Likewise if we parry with our dagger, our left hand should be aiding with grappling or reinforcing the parry.