For a puppy, lying down for waiting is a gesture of absolute obedience, as well, it's a gesture waiting for your command. The puppy may be tense with this gesture, so, at the beginning of training, the puppy can't lie down for long. There are two gustures to lie down, one is lying down in front of owner, another is lying down beside the owner.
When you train the puppy to lie down in front, you should hold the leash in your left hand. First, let the puppy lie down in front of you, then shake your right hand from the top down, and say "lie down" to him. At the same time, pull the leash down with your left hand to hang his head down and lie the whole body down. If the puppy is unwilling, you can pull his collar down. As well, when you give the command, you can pull his forelegs to be straight before lying down, if he get it well, give him nice food as a reward at once.
Similar to above training, When you train the puppy to lie down beside you, let your puppy stand beside your left leg first, then shake your right hand down in front of his head, and say "lie down" to him. At the same time, hold the collar of puppy and pull it down until the puppy lies down.
