There are over 300 types of dog breeds, and as a dog trainer, it can be helpful to understand their personalities. However, even though there are personality traits that are typical to certain breeds, there are exceptions to every rule. When choosing a dog it is important to consider if you will be able to provide for the dog's specific needs. For example, if you are getting a dog that is a working breed, like a German shepherd, border collie or husky, you will want to consider the fact that these dogs need to stay physically and mentally stimulated all day long. If they are not, they can become restless and began to act out. Again, there are exceptions to this and you can still find those breeds of dogs who are content to be lazy most of the day.
People often get smaller dogs thinking that they will be better in a smaller living space. What they don't realize is that a lot of smaller dogs, like Yorkies or Jack Russell terriers, have tons of energy and do better when they have big yards and big home spaces to run around. Big dogs like great Danes or St. Bernards, can tend to be lower energy and will end up cuddling with you on the couch rather than exploring the rest of the house. For this reason they do well in one bedroom apartments.
If you are very active and want a dog that can keep up with long walks and runs, then you want to avoid getting dogs with shorter noses to avoid over heating. Dogs like bulldogs, mastiffs and pugs do not get as much oxygen and it can be dangerous if they exert themselves too much. Also consider if you are adopting or buying from a breeder who is not concerned with maintaining a standard of personality in a breed, your dog can be the exact opposite of what is typical.