How can I prepare my pet for the new baby?

Ask vet. I would talk to your vet about this. I would bring home the hospital blankets that the baby used and allow the pets to sniff before bringing the baby home.
? Depends who is your pet. Birds, reptiles, etc., do not need any preparation. The dogs and cats are usually loyal to children. But it depends from the breed. If your pet is shows sign of aggression or over protection, it's better to check with your vet doctor and to consult the dog/cat behaviorist.