Your dog gives off lots of different signals to you each and every time that you interact. Some signals we, as humans, seem to understand right away and respond to, while others are a bit more confusing and obscure. Being able to read the signals and communications that your dog is sending can help you in responding to your dog and modifying training to better match the dog's natural tendencies and behaviors.
The most common signal that dog's use in interacting with each other, which is the same as interacting with people, is eye contact. There have been lots of studies and research on the importance of eye contact in dog training and how it can be used to evaluate a dog's temperament and personality. Typically a dog that maintains natural eye contact with a person is secure and well socialized and is comfortable with the person. This type of eye contact is often associated with other behaviors such as having the ears back in a sign of friendliness and affection, carrying the head level with the neck or about shoulder height and of course the wagging of the tail, which will be carried in a relaxed and normal fashion.
Eye contact that is prolonged or intense in focus can signal one of two things, either aggression or interest and concentration. Body posture can also help the owner determine this as well. If the dog maintains intense eye contact with ears pricked or alert, head very high, tail very high and stiff and the body as large as possible, this is most likely an aggressive posturing. Of course if the lips are pulled back and the hackles are raised this is a definite and serious sign of aggression and dominance. Dogs that are very interested and focused will still have the high head, tail and ear posture but will typically be more frequently sniffing the air, turning their head to get a better look or circling to try to see what is going on.
Dogs that maintain very little eye contact and have a very submissive posture are often dogs that are nervous, timid or have been abused or mistreated. Often female dogs, especially within particular breeds, are more likely to use a highly submissive posture and lack of eye contact, even with people they know. Submissive urination, often when rolling over onto their backs, is common in very timid males and females. Tails tucked between the legs and a low to the ground head and body position also indicate high levels of submission and possibly fear. Submissive dogs tend to approach from the side or the back and never make a direct straight line type of approach.
Another common form of communication between dogs, which can be used to understand how your dog is feeling, are their vocalizations. Some dogs will be very vocal or talkative while others will only make noises when they are being protective or are feeling threatened. Typically vocalizations that sound like mumbling, yodeling or grunts and soft barks are all signs of happiness, excitement and contentment. Puppies in particular often have a wide range of contented sounds that gradually fade out of their vocal repertoire as they mature. Howling is also a sound that humans associate with sadness, loneliness or unhappiness, however it may also signal "I am here" or be used when there are females in heat in the area to alert them to the male's interest. Some dogs will also howl when they are bored, which is a real problem in urban areas.
Short, high pitched barks typically signal excitement and focus. If you have ever watched a herding dog or seen a dog excited about an activity or even a ride in the car you will recognize these short, happy barks. These differ in tone and length from barks used to alert other about the presence of a stranger or something out of place. These barks tend to be longer, deeper and more intense in sound. Some dogs may even growl in between these types of protective or defensive barks.
Dogs also send what are called "calming signals" when they sense that their owners are upset. Calming signals can range from yawns through to whines and avoidance of any type of eye contact. Often you will see these behaviors if you verbally scold or correct your dog. He or she will look away, lie down, pretend to go to sleep or slink off into another room. All these signals in a pack of dogs would indicate that the dog understand you are upset and is trying to act in a way to calm you down, preventing any further escalation in your aggression. If you are correcting your dog and you see these behaviors, they have got the message and you need to stop and just ignore the dog until you want to make positive contact again.
Contrary to what many owners believe, there is little evidence to suggest that dogs feel emotions such as remorse, embarrassment, sadness or even jealousy. People often impart these emotions to their dogs based on how their dog is acting. For example, if your older dog gets upset when you pet your new puppy, it is not likely that the dog is jealous in the true sense of the word. The fact that the older dog wants attention when you are petting the puppy is more likely a result of the puppy jumping his or place in the hierarchy of the pack. If you were to pet the older dog first, then the puppy, it is much less likely the older dog would act what we perceive to be jealous. The same can be said about correcting a dog for making a mess in the house. They are not embarrassed or sad because they peed on the rug; they are just avoiding eye contact because you, as the alpha leader, are upset. The dog is not necessarily connecting the puddle with your displeasure, but because of the way you are talking and posturing they know you are angry. They aren't looking at you because to make eye contact would be a challenged, something they definitely won't do when you are already upset.
Watching and observing your dog is the best way to learn how they are attempting to communicate. Once you understand what your dog is telling you, you can then respond in kind to correct the misunderstanding or to reinforce good behavior during training and interactions.