A huge part of training a dog successfully is to have your timing down so that you will reward or correct the behavior at the exact moment it happens. Dogs don't speak our language and you can't spend a few minutes to explain what they have done wrong and how they could do it better.
As the human element of the training it is our job to educate ourselves and practice our technique. You will have to pay close attention to the dog and his/her actions so that you can praise the dog at the precise moment they achieve the desired behavior.
A clicker is a great tool to use to mark the behavior at the exact moment you see it happen. A clicker is used in as a reinforcement tool that emits a sound that the dog begins to recognize as a postive marker that they did what they were suppose to. Training is more about training the human than teaching the dog.