There is nothing inherently wrong with telling your dog “no,” except that it doesn’t give him enough information. Instead of telling your dog “no,” tell him what you want him to do. Dogs don’t generalize well, so if your dog jumps up on someone to say hello and you say no, he may jump higher or he may jump to the left side instead of the right. A better alternative would be to ask him to “sit.” Tell him what you want him to do in order to avoid confusion.
Observational learning is the learning that occurs through observing the behavior of others. This form of learning does not need reinforcement to occur; instead, a model animal is required. While the model may not be intentionally trying to instill any particular behavior, many behaviors that are observed are remembered and imitated. The domestic dog is a social species and its social dependency makes it aware of the behavior of others, which contributes to its own behavior and learning abilities. There is, however, ongoing discussion about how much, and how, dogs can learn by interacting with each other and with people.
A training class is not there to train your dog. Its purpose is to teach you to train your dog so you will need to be committed to train your dog for short sessions (5 minutes) several times a day rather than just simply turn up for classes! This little bit of training everyday will be repaid with a lifetime of living with a well behaved dog. You will also learn to avoid problems before they begin as well as receive help to overcome any that you already have with your dog.