When you look into your pup's eyes, your oxytocin levels rise, just like when you pet and play with him. Show your pup some affection by gently stroking his back or sides, but don't pat him and definitely don't touch his face. If you really want to make your pup feel special, rub his back near his tail; that's his favorite spot to be petted. A tummy massage, a little ear massage, and a scratch on the bottom of the chin, the front of the neck, or the sides of the thighs are sure to bring a smile to your pup's face.
Some people learn how to show their pup love in a formal way, while others simply intuit it as a way of understanding the communication of a non-verbal animal. It's one of those things that seems obvious after learning about it or discovering it.