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.
Relaxed ears mean that a dog is calm. Erect ears show that a dog is alert and attentive. Ears that are up and forward mean a dog is challenging or being assertive or aggressive. Ears that are laid back indicate that a dog is worried or scared.
Play bowing is an invitation to play and a sign of happiness.
Raised hackles indicate arousal, either because a dog is frightened or is challenging another dog. Smooth hackles show a dog is calm.