When you bring home a new puppy it's always an exciting time.
Everyone is excited, the puppy, the kids, and most importantly you.
Your older dog however, may not be so thrilled.
You wouldn't want any kind of hatred built up between the two dogs, and luckily it's fairly easy to properly introduce a new puppy to your older dog.
Dogs, even after adapting to living with humans, have a "pack mentality," where there's a leader (you), a beta, an alpha, etc.
Your old dog is the second in command, the beta, and may feel threatened by the new puppy.
You want both dogs to feel equally loved and wanted.
This will make the transition much smoother.
Make the transition as slowly as you possibly can.
This new home can be very terrifying for your new puppy, and the new puppy can come as a huge surprise to your older dog.
Let the puppy sniff and walk around the home.
Let the puppy get used to his/her new home.
Make sure you stay near the two dogs when they're together- there may be occasional fights and you need to be there to break them the fights up before they get ugly.
Make sure you spend some good alone time with each dog.
This will allow you to effectively have some bonding time with both dogs.
Do this sparingly as it can cause jealously among the two dogs.
Make sure you play with each dog separate, but also incorporate group playtime where you involve both of them.
Once they begin to have fun together you won't even need to be around to initiate it.
Reward each dog for good behavior, especially if they behave with each other during play time.
Once your two dogs develop a strong relationship it'll be cruise-control from there, you won't have to work at keeping the peace anymore.