Certain breeds, such as Doberman Pinschers, German Shepherds, Border Collies, Labrador Retrievers and Golden Retrievers, have reputations as being easier to train than others, such as some hounds and sled dogs. Dogs that have been bred to perform one task to the exclusion of all others (such as the Bloodhound or Husky), or that have been bred to work independently from their handler (such as terriers), may be particularly challenging with obedience training.
You can start training your dog before they're of age to compete. Begin by working on basic obedience and teach your puppy to sit, lie down, come, heel, and stay. Your puppy will also benefit from attending training classes where they will learn basic obedience and get used to working around lots of other dogs and people. Having your pet take and pass the AKC Good Citizen Test is a helpful step.
According to the USDAA, there are over 150 breeds of dogs, including mixed-breed dogs, involved in agility. Some breeds, like the Australian Shepherd and the Dutch Shepherd, are known for excelling at the sport. However, you should not let the fact that you have a Golden Retriever or a mixed-breed dog stop you from trying it. If your dog is playful and energetic, it will probably enjoy agility training.
Remember that training is an ongoing process. You will never be completely finished. It is important to keep working on obedience training throughout the life of your dog. People who learn a language at a young age but stop speaking that language may forget much of it as they grow older. The same goes for your dog: use it or lose it. Running through even the most basic tricks and commands will help them stay fresh in your dog's mind. Plus, it's a great way to spend time with your dog.