It's easy to think that dog training is only for the dog, that really isn't the case. While it's the dog who does the actions requested of them, it's the human(s) who need to decide what they want their dog to do and learn how to have the dog do it. And most importantly the human needs to be consistent. The old saying "if you don't use it you lose it" applies with dogs as well.
Dogs want and need structure in their lives. A dog trainer is an important tool in setting up that structure for your dog. Here are links to the databases of two national organizations of dogs trainers.
Association of Pet Dog Trainers (APDT)
Certification Council for Professional Dog Trainers (CCPDT)
You can also use Yelp to find trainers who may not be members of the above organizations. Regardless of where you find a trainer, we recommend interviewing the trainer to find out their experience. The Association of Professional Dog Trainers has this guide to choosing a dog trainer
Do it yourself dog training
For those who want to train their dog on their own here are some suggested links. Remember, one of the most important keys in training is consistency. The more consistent you are, the more the training will stick. We've included training courses as well.
Books & DVD's recommended by APDT
American Kennel Club courses
the spruce Pets (a sort of guide on how to train your dog. It includes many sub links within this page)
Pasadena Human Society Training Classes