According to Dr. Nicholas Dodman, a well-known behaviorist, make sure the reward you offer in training is the most powerful one for your dog. Food-motivated dogs work well for food, but the treats used should be favorite foods for the dog, such as small pieces of cheese or freeze-dried liver. You want your dog to be strongly motivated to obey commands to receive the treat.
Food treats, if used, should be small – no bigger than the size of your little fingernail. The texture of the treat should be such that it does not require chewing and should not crumble, otherwise you will lose your dog's attention as he attempts to gather up the crumbs. Large treats, like Milk Bones®, take too long to eat, causing the dog to lose attention.
Dr. Dodman has some great tips in this article – please read 12 General Rules for Training Dogs.