Let them meet in neutral territory
Don’t wait until you bring your second dog home for your two pups to meet. Your first dog considers your home as their territory, so they could see your new dog as a threat. Instead, introduce them at a neutral location, such as a park, a neighbor’s backyard, or somewhere during a long walk. Keep both dogs on a leash where they are handled by a separate person. If all goes well, you can head home with you entering the house first, followed by your new dog.
Use positive reinforcement
Positive reinforcement can further encourage two dogs to get along. If they behave well during their first meeting, give them both treats and verbal affirmations. Continue doing this for the next few days or weeks every time that your dogs have a positive interaction with one another.
Keep them separate in the beginning
Even if the introduction went well, your dogs still need time to get used to one another. To prevent any fights from breaking out, keep them in separate areas of the home. Have them meet in neutral territories (again using positive reinforcement when the interaction goes well), and then gradually build up to meetings at home. If these at-home meetings go off without an incident, you can start letting them spend more time together. Just be sure that the dogs are always supervised at least for the first few months.