I was taught that once the dog has "sit" down cold, then you can start with down. You get the dog in the sit position. After rewarding for that, you hold a treat on the ground under his nose. As he goes down to smell it, slowly pull your hand away, still against the ground. The dog will start reaching with his head towards the treat, and hopefully eventually put his legs out. As soon as the dog puts his legs out to lay down, say down and let him have the treat. It worked great with Bogie.