Choosing the right breed of dog for you and, possibly, your family should be done very carefully. You need to analyze what type of person you are, and choose a dog breed that will be compatible and has similar characteristics.
Where do you live? If you live in a small apartment, a smaller breed, such as a type of Terrier, may be a good fit. If you live in the country and have several acres, a large dog, such as a Great Dane, will have ample room to stretch its legs, and may be a possible candidate.2
What is your energy level, and how often are you going to walk your dog? You need to be honest with yourself. If you get home from work, plunk yourself on the couch, and put your feet up for the better part of the evening, then don't get an energetic dog. Rather, choose a dog that is content just being around you, and isn't going to go stir-crazy if he doesn't get two, one-hour walks each day. However, if you love to spend your time being active- hiking, running, and getting out in general, than you may want a high energy dog, such as a Border Collie, that will be a great partner in all your outdoor activities. Just remember, a dog that doesn't get enough exercise is going to get into trouble, so choose a breed of dog that has a compatible energy level.3
Do you have children? Each breed has a reputation of its own. Choose a breed that is calm and tolerant of children. Golden Retrievers are an example of a breed that is known to be good-natured. You also may want to avoid a breed that tends to nip at small fingers.4
Do you have other pets? Think about how well the new dog is going to get along with the other animals. Certain breeds tend to be more dominant, and can become aggressive with other dogs, so if you don't have time to train and exercise your dog to prevent this from happening, choose a mellow breed that is more submissive. Additionally, if you have chickens, cats, rabbits, etc, choose a breed that is less likely to want to chase them. Of course, whatever dog you do choose, you will need to train it, so it doesn't develop any bad habits.5
Do you have allergies to dog hair and dander? There are a few breeds that even people who are allergic to dogs can own because they do not shed as much, such as Wheaton terriers and poodles, or are hairless, such as the Chinese crested breed. This is also a nice trait if you don't have a lot of spare time to vacuum.6
How much time will you devote to training your dog? Certain dogs are more intelligent and easier to train. If you don't have a lot of extra time to train your dog in obedience training, or don't have a surplus of patience, then choose a breed that is more intelligent and easier to train.