Your dog's licks are his way of telling you that he loves you and that he wants your affection and approval. Another reason for licking is that the dog has been unintentionally trained to compulsively lick.
1 Additional Answer
Your dog could be licking your feet for a few reasons. One of the main reasons why they lick is because you have a smell or taste on your skin. Other reasons why include affection and submissive behavior.