First it takes a lot of research. YT is a great place to start learning about the Yorkie and its standard and health issues. You can use the "search" option above in the darker blue bar and there have been a lot of pros and cons threads about breeding. A very important basic consideration is the size of your female. If she is much under 5 pounds as an adult, it really isn't a good idea to breed her. You shouldn't breed until the 2nd heat which puts her over a year old. AKC doesn't accept a litter of a female that was bred under 8 months of age. Know the health risks. Know the signs of problems in whleping. Read as much as possible on whelping. Know what to do in so may circumstances (mother not breaking sack, green discharge, labor but no delivery, pregnant but no labor, shaking/weak female, sac not opened by mother, cord chewed too close, cord not chewed at all, breech birth, dry birth, how to do a proper shake down, the first and last steps to take for a puppy not breathing, how to know if you have a cleft palate puppy, is tube feeding an option, when to take mom and pups to the vet for the first time, how much money to have on hand for emergencies (mine are not even 2 days old and I have $600 into the litter...and that's because I got a GOOD deal), etc.
That's just a few things on your end. Then you have to know much about the stud and his congential and hereditary health issues. It is also very helpful to have someone who has experience be your mentor. You also can't have a weak stomach or a panicky personality. Hope this was a little helpful
.