Structure and rules are very important to a dog, they thrive on it. A dog with a strong leader and solid rules is a happy, well balanced dog who knows his place. If a dog is not given limitations to follow, he will make them himself. A dog without a leader will become leader, and as many people know first hand, a family who is lead by its dog is not a happy family, nor is the dog happy either. When a dog does not have a clear leader to follow, he will take that position himself, this puts a lot of stress on any dog, no matter how dominant it may be. I don't care what people say, but every dog naturally wants to be a follower. It is the healthiest, easiest way to go for them.
If you establish a balanced relationship with your dog, where you are the calm and confident leader, you can then establish communication, and through communication you establish rules and structure.
One of the best ways to help you establish leadership is the NILIF program, which stands for nothing in life is free. It means your dog doesn't get anything he wants unless he does something first. For example, your dog has to sit before he gets affection, or lay down and stay before he eats. This lets your dog know that in order to get something he wants, he has to listen to you and follow your lead, then he will get rewarded.
another important aspect to a healthy, balanced dog is keeping your dogs mind and body active. A dog with pent up energy will be 100 times harder to train than a tired dog. I would highly suggest taking your dog for a long run before trying to teach him anything.
When a dog doesn't have an outlet for it's energy, it will be a very hard dog to handle. A good example of this are working, hunting, and herding dogs who are unable to do the jobs they were bred for. They become frustrated and may start to take out that frustration in inappropriate ways, like herding people or fast moving things, chasing animals and digging, and many other (often) bread specific problems. These dogs need outlets and a job. Something as simple as making your dog fetch the newspaper every morning, or carry something on walks everyday, can help with these problems.
Overall, structure and rules are the basis for a mentally stable dog who is well behaved and happy.