Believe it or not, dogs can smile just like humans. During everyday life, when Max is happy, you might catch him with a relaxed body posture and a big grin on his face. Just like how you teach Max to sit, come, speak and stay, you can teach him to smile on command. This makes for great photo ops and allows you to enjoy his smile at the drop of a dime.
Arm yourself with dog treats and sit across from your dog in a quiet area that's free of distraction so you have his undivided attention.
Push his upper lip up above his gum line with the thumb and index finger of your dominant hand. Mimic the motion you would make if you were inspecting his gums and teeth. Then say "smile" while you're holding his lip in a smiling position. Put a smile on your face too, to encourage your pet companion to copy you.
Repeat this several times, and immediately after each time you help him smile, say "good boy," and reward him with a treat. Consistently do this so he associates curling his lip back with pleasant consequences and is encouraged to repeat the smiling motion.
Continue to teach Max to smile during everyday situations. If you know that your pet companion smiles when he's scratched in a hard-to-reach area, scratch him and say "smile." When he smiles, give him treats and praise. Do this each time a situation emerges in which your dog might naturally smile, and always use the same command to avoid confusing Max.
Practice the "smile" command daily for several minutes at a time, and lavish Max with praise and treats when he smiles on command. Over time, gradually decrease the amount of treats you give Max. Give him treats after every third or fourth smile so he'll continue to smile in the hopes of getting a possible treat.