If only they could talk! You may be surprised to know that your dog can communicate with you very well, but he just doesn't use words. He speaks "body language" and by watching his eyes, ears, mouth and tail, you can learn to interpret what he is saying to you.
1. Eyes. A direct gaze indicates a confident, assertive dog. If he is nervous or submissive, he will look to the side or down at the ground. Watch him when he interacts with other dogs or people, and you'll get a good idea about how he feels towards them.
2. Ears. When you are assessing your dog's ear position, look at the bottom of his ears where they are attached to his head, rather than the ear flap. If it is held forward, he is watchful and alert, and interested in what's happening around him. If his ears are back, he is feeling afraid and possibly even defensive.
3. Mouth. It's easy to recognize a relaxed happy dog, with their open mouthed smile and lolling tongue. It's just as easy to identify an aggressive dog, as they bare their teeth. You can see a more subtle indicator of your dog's demeanor by looking at where his upper and lower lips join at his cheek. If it is pulled back, it is a sign of relaxation or submission. Held forward, it indicates that your dog is alert and watchful.
4. Tail. A wagging tail isn't necessarily an indication that a dog is friendly. It just shows that the dog is willing to interact in some way. A tail that is tucked down between the hind legs belongs to a frightened submissive dog. If your dog holds his tail high, he is feeling confident and assertive.
In Summary - If you put these indicators together and you can get a good idea of how a dog is feeling, and what they are likely to do. If a dog is showing that they are frightened, with tucked tail, ears held back and a wide-eyed gaze, they may bite purely out of fear. Alternatively, a dog who has a wagging tail, ears held forward, and whose mouth is relaxed, is very likely to be keen to say hello.