Before you breed your Yorkie, you need to decide whether or not she is a good candidate for breeding. No female should be bred before the age of 2. She is not physically nor emotionally mature enough. She needs to grow and develop her reproduction system before going through the physical exertion of breeding and whelping puppies. You should be preparing her for breeding from the time she is a pup. Provide her with quality nutrition and good health care. I use an excellent quality brand of foods.
Obedience training can be indispensable. There are times when a female will get overly anxious when her new puppies start crying. Being able to put her on a down and stay can allow the puppies to get to their food at her belly with less anxiety. This can give you and your Yorkie peace of mind.
Your Yorkie should be well socialized. She will be a happier Yorkie if she has activities in her life and goes places with you and does fun things. If she is happier, she will make a better mother to her puppies. You should take your female to other breeders or, a better choice, start showing her in CKC events. The best way to ensure that you are improving the breed is to breed quality Yorkies with other quality Yorkies, minimizing faults and strengthening good qualities. We all love our little girls but you will need to look long and hard at her and decide if she's really worthy of breeding. Sometimes, as Yorkie owners, we don’t see the flaws that our Yorkies have. CKC events give us a better idea of whether or not our dogs are worthy of breeding. Some people won't breed a female until she's earned her Championship in the show ring. If you aren’t willing or cannot show her, then at least have her evaluated by another, more knowledgeable person. Any experienced Yorkie show breeder should be able to help you evaluate your female honestly.
Health care is essential. Ensure that her teeth are well looked after so she won't get infections and become weak. Pregnancy, delivery, and puppy raising are very stressful on a Yorkie and knowing that you love her, combined with good health care, makes whelping her puppies a happy and less stressful event. She'll trust you to help with the puppies instead of feeling that she must defend them. You will need to have various health checks done in order to determine whether or not your dog should be bred. Very important! You should consult a good book on Yorkies or ask a knowledgeable breeder to determine what tests you'll need to have done. You can find some info on my Yorkie Health Page. Many believe that Liver Shunt testing should be done because of the rise in numbers of small breed dogs who contract this probable hereditary disease.
You should request testing from the stud dog owner as well as providing your results to them.
Information gathered off the WWW, books, experience and advice.