Overcoming your dog’s natural reluctance with trust
Understand that to teach your dog to lie down is one of the most difficult for them to accept. The “down” is considered a yardstick to judge your dog’s inborn personality because from your dog's viewpoint this position is submissive and showing submissiveness is something that some dogs are reluctant to do.
A timid dog will roll over, which is a natural gesture of submission whilst a bolder pup will want to get up and might back off, not wanting to submit. The dog will feel as though she's about to be punished, which would be the position in a natural environment. Once your dog understands this is not the case and that there are rewards for obeying, she will accept this position.
You may notice that some dogs will sit very quickly, but will respond to the down command more slowly. It is their way of saying that they will obey the command, but under protest.
With a puppy or a small-
The dog should follow the treat with her head. Bring the treat out slowly in front of the pup. If you are really lucky, your dogs legs will slide forward, and she will lie down. Give her the treat and lots of praise for being such a good dog.
For a dog that wont lie down on her own (and most will have trouble doing it), you can try this method: After your dog is sitting and focused on the treat, take her front legs and gently sweep them forward, at the same time saying, "Down."
Release the legs and quickly apply light pressure on the shoulders with your left hand. Then tell the dog how good she is, give the treat, and make a lot of fuss. Repeat two or three times only in one training session. The pup will learn over a few lessons. Remember that this is a very submissive act on the dog's behalf, so there is no need to rush matters.
One handy tip to help with teaching the down command is to keep your dog’s lead attached to the collar because if you need an additional tool for a dog who is less than willing, you can hold the lead right down on the ground under mild tension -
For some great home training aids -