Introducing your dog to another pup who will be spending time in your best friend's territory (your home) can go terribly wrong if not done properly. This is my super easy three-step approach to a proper introduction to ensure a long lasting friendship.
(1)I always think the best way to find your pup's new playmate (and pup swapping partner) is in a place with a few dogs, off leash and in an inclosed larger area, like a dog park, a pup social or at a Pup Mixer hosted by Pup Sit Match. Woof, I like that last one. During this first step of the meet and greet process you will see first hand who your dog gravitates towards, plays well with and whom they do not.
(2)Once you've identified a potential match for your pup, arrange to take a walk with the other pup and pup parent. This second step of the meeting process has two purposes. First, it is a signal to your dog that you are not threatened by the other pup or pup parent, therefore they don't need to aggressively defend you. Second, it gives the pups something to do together that they enjoy without the pressure of trying to find common ground on this first date. you've decided who might be your pup's long term pup match, arrange to meet, just the two of them, in a neutral place within walking distance of your pup's residence; perhaps your front yard or the common area of your apartment complex.
(3)This last step of the meet and greet process will be to welcome your pup's new friend into your home, preferable as you are finishing up your walk. Once you are safely in your home with the door shut (safety first!) take off the dog's leashes. As a pet sitter I have conducted hundreds of meet and greets and have found that a dog being on a leash in an enclosed space incites aggression. Let the pup's play and roam around your home, while you and the other pup parent are supervising. If there is a scuffle, resist the urge to pick up your dog. By doing this you are signaling to your pup that some how they are at fault and or there is reason for them to be concerned about their safety. By far most of the time pup's will get over their territorial disputes on their own without much more that a firm 'no' by you.
Introducing a New Dog to your Resident Dog, PetMD
Introducing a New Puppy to your Dog, FidoSavvy
Introducing a New Dog to your Current Dog, The Ohio State University, College of Veterinarian Medicine.