Bringing a new dog into your life is a super exciting experience, but one that can be met with some added stress if you already have a dog at home. You might be worried about how the two dogs will get along - from sleeping to playing to eating to fighting for your attention. If you don't know where to begin, here are some tips on how to make that initial introduction between your new dog and your current dog go smoothly, along with some ideas for the first few days.
Tire out the two (or more) dogs ahead of time - Take each of the dogs on a long walk or for some play time in the dog park before introducing them. Expending some energy along with the socialization will mellow them out before the full introduction and you're more likely to get a calm interaction.
Choose a neutral location for the introduction - Okay, this sounds counterintuitive since the core question is how to introduce your new dog into your home with an existing dog, but an introduction in a neutral environment is the most non-threatening place to start. So have them meet outdoors, have each dog walked separately on a leash (you should probably bring along a friend, partner, neighbor, whoever it is to help out) and keep some high value treats and rewards handy.
Leverage positive reinforcement - With the dogs on their leashes, they'll probably start circling and sniffing each other. Now's the moment for those high value treats and rewards. If the dogs aren't provoked by each other and aren't causing a big scene, start dishing out those treats along with a bunch of 'good boy!' and "good girl!" comments. Reward even the smallest mellow moments to reinforce that each dog isn't a threat to the other and that calm, friendly behavior is the way to go.
If you're not sure if things are going that smoothly, here is a list of behaviors to watch out for, along with how get the dogs back on the right track.
Give them each their space - Alright, so they've met out in the world and they seem calm around each other (or calm-ish.) Now what? It's time to head home. And though you might be taking them back to a small apartment, if you can manage it, letting each of the dogs have their own space to unwind and relax will make a world of difference. Whether that's a crate or baby gates or sleeping in separate rooms, you can minimize a lot of their indiviudal stress if they feel like they have a safe space that's theirs. Also, try to avoid free feeding in the beginning if that's your thing. Give them each their own meals in their own space to minimize the threat of competition.
Pay close attention for the first 24-48 hours - This sounds obvious, but the first day or two are the most important. If you can be there firsthand to see how they're adapting, to see if there are any altercations or visible signs of stress, then you can be there to step in.
And last thing, we can't tell you enough just how jealous we are that you now have two dogs in your life. You're really living.