Start somewhere quiet
Put a non-slip mat in a familiar room. Reward your dog for choosing to approach it. Avoid pulling the dog onto the mat or forcing a lying position.
Keep success small
A paw on the mat is a useful beginning. Gradually reward a moment of staying there. End with a break before the task becomes frustrating.
Change one thing at a time
Once the dog is comfortable, try a small distraction such as taking one step away. If the dog gets up or becomes watchful, make the exercise easier. Never insist on staying in a stressful situation.