Pawing is an appeasing gesture. Licking another dog's face is an invitation to play or sign of deference.
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.
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.
A relaxed tail means that a dog is calm and at peace. A tail head straight out, wagging rhythmically and slowly, means that a dog is cautious or on guard. Tail down indicates worry or uncertainty.