Dogs and humans are both social animals that look to the dominant member of their society for direction. That is one reason that the two species can co-exist so well. A human that can establish himself as dominant in the eyes of a dog can train and influence it to a great extent.
The natural instinct of a dog is to try and please the alpha member of the pack. That behavior makes dogs easy to train. They don't care how strange the trick is that we want them to perform, the dog just wants to keep the pack leader happy.
Sit, stay, and heel are basic things that a person will teach a dog. Once those basics have been established most dogs will continue to learn additional commands.
The hard part for the trainer is getting a dog to connect a behavior with a command. Dogs that naturally paw at a person for attention can easily be trained to shake, we simply need to connect the word with the behavior that the dog is naturally doing.
Clicker Training is a type of behavior conditioning which gets the dogs attention when it performs a desired activity on its own. When the desired behavior is done the trainer will use the clicker, state the command to be associated with the behavior, and present the reward. The dog will quickly associate the command, action, and treat at which time the clicker will no longer be necessary.
Positive reinforcement is the easiest way to get the dog to associate words and actions. Dogs want to please, and a simple "Good Dog" or treat is all the positive reinforcement that is normally required. Some dogs respond better to a ball or other object, but the basic idea remains.
When you combine a dogs natural desire to please with an innate intelligence, the number of tricks a dog can be taught is limited only by the imagination of its owner. This can cause problems when we unknowingly encourage unwanted behaviors. Something that is cute in a puppy can be threatening when done by a full grown dog.
It is always best to begin training at a young age. The younger the animal is when training begins, the easier it is to establish yourself as a dominant figure. Puppies are easily distracted, and like young children cannot handle long training sessions. Scheduling frequent but short training sessions will not keep the puppy interested and the trainer more patient.
Repetition, patience, and consistency are the keys to a happy relationship between yourself and your pet.