Your dog licking you is probably a means of affection. Otherwise, it might be because you have something tasty on your hand. There are ways to train your dog to stop (saying "no lick" with a stern face when they try, turn away from them and/or ignore them, spraying them with cold water). However, it may be that your dog has a lot of stress or is lonely, and is licking you because he or she wants more affection and attention. Find the source of the problem and it'll be easier to fix.
To stop your dog from licking you, you can simply try ignoring your dog or walking away from your dog every time he starts licking you. For more information and techniques to combat excessive licking, check out this site - http://www.stoppingdogproblems.com/stop-dog-licking/