Introducing a dog to other pets can be a challenge. Here's everything you need to know about this socialization process.
Initial Introductions
Domestic animal encounters will vary depending on the type of animals being introduced, as well as the size of each animal. Carefully orchestrate the initial encounter. For instance, if you are introducing your Great Dane to a new kitten, it is wise to hold the kitten and encourage a calm and controlled first meeting. Even if your dog isn't aggressive, she may not realize her size can be both harmful and frightening to a smaller animal.
It is also important to consider the personality types of both the dog and the other animal. Is your dog aggressive? Friendly? Submissive? Is the dog old or young? Has she successfully lived with another pet in the past? How about the other animal?
Upon the first encounter, your dog will probably show some territorial behavior along with signs of jealousy. This will subside with time if she is allowed to gradually become accustomed to having another animal in the house. Give both animals time to meet each other and learn what it will be like to live together. In most cases the animals will become companions rather than enemies.
Things to Remember:

Advantages to Having Another Pet
Dogs are naturally dominant, causing them to often times wield power over another pet. A dog that shows initial signs of jealousy will usually get used to the idea of having another animal in the house. This can be advantageous in circumstances where the dog is left alone for long periods of time. A new pet can be a relief from the boredom of being along all day. This can also decrease the amount of human attention the dog requires.
Positive Reinforcement
Encourage your dog to accept the new pet with positive reinforcement and treats. Show your dog that the new pet is an addition to the family, not a replacement for her. The relationship that will hopefully form between the animals can be a life-long friendship to be enjoyed by the entire family.