This is great for impulse control, helping them relax and learn to stay in one place. It helps with skills such as settle, sending to bed and stay.
From sitting: hold your treat in front of their nose. Move it slowly down towards their front paws and slightly forward. When their elbows touch the ground, mark and reward.
From standing: move your treat from their nose back between their front legs. They’ll likely lower their head, nibble and fold into the down position. As they do, mark and treat.
As with teaching a sit, add your cue on at the beginning when they are reliably lying down. Once you have your cue on, it’s time to start fading the treat out.