To take care of a Shih Tzu Chihuahua mixed breed puppy you need to be sure to have puppy chow, a bed, some toys, and some grooming materials. If your puppy has not had its shots yet then be sure to schedule an appointment to get those out of the way. You should also talk to the vet about spaying/neutering your dog.
You would take care of a shih tzu chihuahua puppy the same way you would take care of any puppy. It will need puppy food at least two or three times a day. If it is a long haired puppy, you will need to make sure to groom it regularly.