Introducing a second dog into your home can be a decision filled with joy and laughter or turn into an emotional rollercoaster that leaves you with one unhappy animal and the potential for ruination of your current household items. The key to bringing a second dog into the home lies in preparation that takes several aspects of the decision into consideration.
Consider the bond between you and the current dog, for instance. Dogs have a tendency to either bond extremely closely to their owner or to barely give you a look whenever you leave or return home. If the relationship between you and your dog is akin to the relationship between a parent and child, the very idea of introducing a second do into the household is one that should be considered with a healthy does of wariness.
Another consideration is the bond that may or may not develop between the dogs. Again, some dogs are able and eager to bond very closely with another dog while some dogs will never truck with an interloper. The best tactic you can use to help facilitate the bonding process between two dogs is to separate them from each other whenever you are away from the house. Either put one in the yard and the other inside or leave them in separate rooms or place a partition in your yard. The point is to keep them from socializing with one another unless you are present to supervise activity and make sure that they get along. You should also take each dog for a walk or drive or activity outside the house separately at first. This will allow you to focus your attention on just one dog and thus keep the other from becoming emotionally shattered if you were to do the same in that dog's presence.
When you do bring the second dog home and make initial introductions, do so with care and awareness that dogs don't bow to each other and hand over their business card. The canine equivalent of this human introductory ritual is the act of sniffing the other dog's butt. Some first dogs are more likely to bite or nip or bark than others, while some dogs seem to be overcome with joyous abandon at the prospect of a friend to play with.
Finally, when introducing a second dog into your home you want to make sure that you give the new relationship enough time to mature. Dogs sometimes take a while to get used to both other dogs and human beings. Make the transition easier by supply the new dog with his own food and water bowls and toys. Make the effort to emphasize your current dog's position as the leader of the pack. This can be done by choosing to feed him first, play with him first and otherwise giving him the attention necessary for the second dog to pick on the signals that he is not the Alpha dog.
Good luck and remember, above all else, to pick a second dog that is suitable for companionship with your existing animal. Do the research to find out which particular breeds are most compatible with each other and which breeds are particularly incompatible.