Tips for Motivating Your Dog for Training
According to Dr. Nicholas Dodman, a well-known behaviorist, ensure that your dog's motivation for reward is highest during a training session. If food is the reward, train before a meal, not after. If praise, petting and other aspects of your attention are to be used as a reward, schedule the training session at a time when your dog hungers for your attention (for example, after you have returned from work).
Dr. Dodman has some great tips in this article – please read 12 General Rules for Training Dogs.