Get a treat, show it to the dog and then make fist, closing the treat in your hand.
Hold your fist out in front of the dog. The dog will begin to experiment to see what works to get the treat out of your hand (usually sniffing, licking, etc.). The second the dog goes to paw at your hand, click and open your fist to release the treat.
Step Two: Repeat it
Repeat until your dog immediately goes to paw at your hand when you close your fist and hold it up.
Step Three: Cue
At this point you can add the verbal cue. Say the command “shake”, wait one second, and then hold your fist up like you have been.
Step Four: Practice!
Once the dog is successfully pawing at your closed fist, practice without the treat in your fist. Instead, treat from your other hand.
Slowly begin to open your fist to be an open hand instead of a closed fist.
Remember that dogs do not generalize so if you practice while you are sitting on the ground he will struggle once you begin to practice standing up
If your dog is struggling to lift his paw you can move your fist around and try to entice him by saying “get it!” or “here.”
You can also try to nudge his leg with your fist. Once he lifts his paw, click and treat. Slowly shape the behavior from there.