TIP #1: A WAGGING TAIL DOESN'T EQUAL A HAPPY DOG
A dog that is wagging his tail but barking with a defensive body posture, tense face, and hard staring eyes is overly aroused and frustrated, which means that he should not be approached.
- Victoria Stillwell
TIP #2: HOW YOUR DOG SEES YOU MATTERS
Your dog will watch you to read your body signals and he'll quickly learn what your're feeling even without you speaking. If you want to improve communication with your dog, improve your own body language. For example, crouching down with arms open is a welcome sign while towering over him and staring is a sign of threat.
Jeff Dentler, CPDT-KA, IAABC-ADT, FFCP, CTDI