How should I introduce a new pet to the other pets in our home?
Sometimes your existing pet and your new pet will get along swimmingly in just a couple of hours. But you should not be surprised to have a battle on your hands if you try to introduce your new pet too quickly.
The time you spend on this all-important process will be saved exponentially by not having to break up conflicts every day. Also, the first couple of weeks can set the tone for the relationship for a long time to come, so "getting it right" the first time will save a lot of hassles later on.
Keep in mind that a successful transition can take anywhere from two hours to six months, so don't be discouraged if your pets don't seem to get along well at first. Often the case is that they will eventually be "best buddies."
Because there is such extensive advice available on introducing a new dog to an existing cat, a new dog to an existing dog, or, a new cat to an existing cat or new cat to existing dog, I’m going to recommend you visit the following Humane Society of the United States’ links to get advice specific to your situation.
Introducing Pets to a New Dog
Introducing Pets to a New Cat