The command “side” is used for a dog to roll over onto his side.
To teach the dog to lie on his side:
Step One: Lure
With the dog in a “Sit,” hold a treat in front of his/her nose, then lure SLOWLY straight to the floor at the dog’s toes (dog moves into a “Down”).
Step Two: Mark & Reward
Continue luring the dog over onto his side by moving the treat over the dog’s shoulder. Mark (click) and reward when he shifts his body even slightly.
If possible, lure until the dog lies his/her head to the ground too, but just lying on its side is good enough to click and reward. Then you can shape the behavior from there.
Practicing this on a blanket can be helpful sometimes – some dogs respond better on soft surfaces.
Step Three: Repeat it
Repeat until you get a side several trials in a row. When your dog starts to go into the side very quickly, it is time to start using the command and removing the food lure.
Step Four: Cue
Once luring is consistent and the dog lays right onto his side, add the verbal cue, “Side.”