Most ferrets don't get along with birds, fish, rabbits, rodents, lizards, and the like, though there are some exceptions. For a dog or cat, patience is the most important part of the introduction. Give the new animal a chance to get used to you and your home before introducing it to the other pets one at a time, very slowly.
Cats Cats are generally less dangerous than dogs, simply because of their size.
Over the next week or two, gradually give each animal a bit more freedom, watching them closely, until they're used to each other. Once you're convinced that they're used to each other and get along all right, let them interact freely, but supervise them for a while to be sure. Make sure the ferret has an escape route, a barrier the cat can't get through or a safe hiding place. It's generally believed that ferrets get along with cats better if they're introduced when the cat is still a kitten and is more willing to play, but there are plenty of exceptions. The same is probably true of dogs.