Panting means that a dog is feeling playful, excited or stressed, or he may simply be hot. A dog with mouth and lips closed is uncertain or appeasing.
Mounting or standing above another dog by putting front paws on the other dog's back means asserting dominance. It isn't just a male characteristics for females do it too. Mounting is more often related to social status than to sex.
Paw lifting is a dog's way to call your attention. It may be an invitation to play or a means to tell you something else.
Tail held up and wagging fast indicates excitement. An erect tail is a sign of alertness. A tail held between the legs is a sign of fear.
Direct eye contact means that a dog is feeling bold and confident. Casual eye contact means he's contented. An averted gaze means indifference. Dilated pupils indicate fear.