Buying a puppy is a serious commitment and should not be taken lightly. Before making that decision consider whether you have the time and money to care for a dog properly and the commitment to do so for the rest of its life, which could be 15 years.
If you decide to get a dog why not consider giving a home to a rescue dog? Animal shelters up and down the country are full of dogs needing a home. Rescue dogs make wonderful companions and desperately need our help since thousands are abandoned every year, in many cases through no fault of the dog. Many thousands are put to sleep simply because they don't have a home; so when you give a shelter dog a home, you're literally giving them a second chance at life.
If you have a particular breed in mind you could also consider adopting from one of the many breed rescues but always do your homework and checkout the people who run the rescue are reputable.
Never buy a puppy from a pet shop, most pet shop pups are from puppy farms. This has been proven time and time again. Never buy from anyone who advertises with only a mobile telephone number as this indicates they do not want you to know what area they are in and often want to arrange to meet you somewhere. Buying over the Internet is also very risky,breeders websites look good but can be very deceiving. Never buy from anyone who breeds more than one specific breed or who has pups for sale on a regular basis.
If you do decide to get a puppy from a breeder, you should first research which breed of dog will best suit your lifestyle. Buy your puppy from a responsible breeder,raised in a home environment so puppies are socialized. Make sure you see the mother with her puppies and check she appears healthy, with good temperament and that her puppies are fit and healthy. Never buy a puppy less than 8 weeks old. Ask to see proof of health testing for the breed you have chosen to ensure the chances of genetic diseases, which are common in pure bred dogs, have been minimized. A good breeder will ask you lots of questions, will welcome questions from you and should offer full support when you take your puppy home. He/she will agree to take the pup back if things don't work out.
Good luck in your search and please make sure that you do not contribute to the cruelty that dog breeding has become.