Before committing to purchase from a breeder make sure you see the following:

A minimum 5 generation pedigree, a decent breeder will know his/her lines so can easily email you a copy.
 
All Health Certificates for Sire & Dam, if they have not had a minimum hip scoring for both and haemophilia testing for the male go elsewhere (preferably elbow scores as well).

Check scores of sire & dam’s siblings and previous progeny. Make sure the pup will be registered on the Breed registry, not the Activity or Dog lovers Registration.

See the pups and Dam, and if possible see the Sire, although not all will have the Sire in their kennels. If possible see other relatives, go off recommendation if you can.
 
Please make sure you research the breed, too many end up in rescue kennels due to the owners not having a proper understanding of the breed. What do you want the dog for is it a companion or do you want it for a particular sport, if so what happens if it doesn’t make the grade are you willing to keep it? Will the dog fit in with your lifestyle? If the answer is “no” don’t buy one.

Be prepared for necessary veterinary bills, vaccination costs, preventative treatment, health screening. Be prepared to be asked questions by the breeder and ask questions you need to know.

Once you have committed, find out what the breeder uses for food and buy some before you bring the pup home. Don’t change diet in the first few weeks as it only adds to the stress. When/if you change do it gradually. Buy other essentials collar/lead/bed or crate etc. Research dog clubs in your area, and visit some before getting the pup. That way if you like the way they train you can put your name down on their waiting list.