When introducing new pets to one another, it often works best to choose neutral territory to avoid unnecessary disputes right off the bat (this is especially true for males!). What qualifies as neutral territory can vary on the animal, for dogs it may mean choosing a place away from the house, such as a park or even the sidewalk a little down the street. For smaller animals, such as hamsters or rats, a bathtub works well.

Next, if the animals are getting along well in neutral territory, then it's time to introduce them slowly into what will be their standard setting, be it your house, or living in the same cage. If they'll be sharing the same cage, you should first clean it out thoroughly (toss the bedding) and wash all of the food dishes, toys, etc. to help remove some of the original animal's territorial scenting. For larger animals, such as dogs, make sure that the new family member has his/her own toys, food dish, and sleeping area, to avoid fights there. Make sure to keep an eye on them for a few days after the introductions, to make sure they're still getting along. If not, they should be separated to avoid anyone getting hurt, and then re-introduced again.

Some animals will get along right away (introducing a younger pet to an older animal tends to be easier, as the older animal does not consider the younger one to be a threat to its pecking order), others may take longer to acquaint to one another, so have patience, and remain calm. If your first animal senses your frustration, they may "blame" it on the new family member, which will only further aggravate the situation. In time, once pecking order squabbles have been resolved, they may become the best of friends and learn to enjoy each other's company. Good luck!