Dogs can mean a lot of different things when they lick your face.
When your dog licks your face, he could be trying to send you a message, gather information about you. If your dog is nervous or anxious, or fears that he has made you angry, he may try to lick around your face to make up with you, or he wants your attention.
A dog licking your face is expressing his affection for you and trying to strengthen the familial bond he has with you. When your dog lick your face, he may be communicating that he except you as the dominant pack leader.
If your dog licks your face around feeding time, he may be letting you know that he is hungry. If your dog licks your face, he may be grooming you to help keep you clean. He may simply be enjoying the saltiness of your skin.
Your dog may lick your face simply because it feels good.
When a dog tries to lick your face, you can close your eyes, yawn and turn your head away. In dogs’ language this shows that you accept its offer of friendship.