When I took my oldest dog to obedience training, the trainer had this advice:
1. Issue the command to your dog, and if he obeys, reward him sometimes (all the time in the begining, and then you gradually ease off on the positive reinforcement until it is more sporadic).
2. If the dog does not obey, then pull quickly on the leash to get his attention, and then say "No" before you issue the command again.
3. Do not keep doing this over and over. After saying no and issuing the command, if the dog still doesn't obey, it's time to figure out something else because if you keep saying it over and over, you are just nagging the dog, and he will learn to tune that out very quickly.
Humans can learn a bit from trying to train dogs
M-47,W-40,No kids D-filed 5/27/2010 Piecing - 10/21/2010 -=Soon to be banned=-
