Many humans, especially those from the lower classes (check the Identification Guide in Chapter 2 to determine the likely status of your human), respond well to food as a training motivation.  Starvation does not hurt them, and after a day without a meal they will prove even more attentive and responsive to commands.  Even the lowest humans seem to prefer cooked food, however, so be sure to take the time to heat any meat you offer them, or they may feel repelled rather than rewarded.  It is also a good idea to secure any stored food you keep in the lair, to prevent the human from finding its own meals during the training process.