You have to arrange for a male mastiff and a female one. If you have one of the genders, borrow another from a friend. You can also consider paying someone for borrowing or buying stud. Some people just want a pick out of the litter. Make sure that both the parents are mastiffs. Look for breeding dogs in excellent health so that there are no genetic defects in the litter. You can also avail genetic test for different health problems common in mastiffs like heart and eye issues. Mastiffs also commonly suffer from hip and elbow dysplasia. Since mastiffs are such a great breed, its worth the effort. Mastiffs can be bred only after they are eighteen months old.
You have to mate the male stud with female mastiff when she is during her heat cycle. You can also arrange for artificial insemination with the help of a veterinarian. It is better to take advice from professional breeders before deciding to artificially inseminate.
Take care of the female mastiff during pregnancy and provide ample nutrition and food. It is better if you have a veterinarian called in at the time of birth, should there be any complications. Once the babies are born, make sure they receive all the necessary immunizations and injections. You can also sell the puppies to interested buyers through advertising or word of mouth. Mastiff is a breed which is always in a great demand so you will not have much problem with it. However, raising mastiff babies with all the medical care involved can be costly.