Now is the time to ask yourself these questions. This will permit you to avoid many problems, either in selecting the right breed, or in learning to educate your animal appropriately. The fact of already having a dog might influence your choice. Indeed, the 2 individuals should learn to cohabitate. Some breeds are very dominant and territorial, risking conformations sooner or later at the time of establishing the hierarchy.
Some breeds are, on the other hand more tolerant.
Again, every individual has a different character, you will need to evaluate all possibilities. Socialization and obedience are probably the two essential points in this case. In general, males are bigger than females of the same breed. According to certain authors, they would also be more outgoing. Others think that females are more loving, more affectionate with children and stay more attached to the home.