You can also lure a down from a sit or stand by holding a treat in your hand to the dog’s nose and slowly bringing it to the floor. Give the treat when the dog’s elbows touch the floor to start. After a few practices, begin bringing your empty hand to the floor and giving the treat AFTER he lies down. When he can reliably follow your hand signal, begin saying “down” as you move your hand.
Always remember that you are dealing with a very immature young animal. Be realistic, flexible, patient and always fair during puppy training sessions. Your puppy doesn't just automatically know this stuff! It's all new to him and he is bound to have the odd slip up and mistake along the way. Don't worry about these mistakes, just move on and do your best to prevent them in the future.
Just as a child needs a caring parent; an athletic team needs a coach; your puppy needs a leader and a clear social hierarchy. If you do not take up the role of leader, your dog will; and you will end up with an unruly, disobedient dog. Many people try to win their new puppy's love by letting the puppy always have its way. Buckets of affection is a wonderful thing for most puppies, but it must be tempered with respect.