1. Wagging tail = energy ... could be happy or angry
2. Barking = pay attention ... could be anger, fear, lonely, happy, friendly
3. A dog looking at you with soft eyes and mouth a little open is smiling
4. A dog that licks his lips or nose may be uncertain about the situation.
5. A dog that yawns may not like what is happening.
6. A dog that shakes off is changing his mood.
7. A dog that has his elbows on the ground and butt in the air is doing a playbow. If the forelegs are spread apart, he is probably ready to play. If the forelegs are straight, he may want to play, or may be saying that he is not a threat.
8. A dog that is staring at you hard or even away is a dog to back away from. A dog that looks away does not want to engage.
Go to a dog park and look for these behaviors... and write down what you see...
There are about 30 'subtle' behaviors called Calming Signals. And, I believe there are fewer than 100 other behaviors.