Most dogs will pretty readily accept the new pup, but to help the getting aquatinted process a few things may help. Start by putting the new pup in his crate where the old dog can sniff and check him out through the bars (for those with out a crate considering using baby gates to keep the dog and pup separate while allowing the getting to know each other sniffing. Alternatively - have someone hold the pup while allowing the older dog to sniff the pup, possibly with someone else restraining the older dog if a problem is anticipated). Once the old dog has accepted the stranger in the crate without aggressive behavior (if aggressive behavior is exhibited - leave all meeting for while on the smell through the bars stage ), the next step is to allow a nose to nose meeting. Most pups will want to play. Most older dogs will take the position of "where did this bundle of energy come from?" and either play some, stand stoically or walk off growling and warning the pup not to come near.
For the dog that warns the pup not to come near - allow some time - as the pup will get the idea after a few snaps and growls to leave the older dog alone for now. As long as the older dog does not actively attack the pup with harm in mind you are fine ( this is rare - and the pups maturing usually takes care of the problem ).
For older females not accepting the new pup it may help to rub the pup around on the female to transfer some scent. For either sex a bath for both may temporarily help establish a mutual smell. Never leave the pup unsupervised until you are completely sure of your older dog.
For those that play right off the bat -- great -- it is more the normal thing.
Be sure to give equal if not more attention to the old dogs to prevent feelings of jealousy. Yes, you will want to play with the newcomer. That is natural be please remember the older dog. The pup will revel in the attention but does not know when attention is being diverted like the older dog does.
Pups will learn from the older dog - that is natural. If your older
dog
has bad habits be sure to watch your pup and correct him while he is
still
learning. Fr the older dog that knows the household routine and is good
with
it that can only help you training your pup.
I have watched older dogs house train entire litters to a doggy door.
When starting obedience training be sure to include the older dog. If he already has basic training the pup can learn a lot by example and your older dog will not feel left out. If the older dog does not have basic then they are learning something together. (note, if your old dog is to old for the workout or is a really slow learner you may not want to embarrass him in front of the pup )
Young pups can bring out a playful exuberance that you may not have seen in your older dog for sometime. Two dogs playing together can help keep both physically and mentally fit. Make sure they both have adequate toys and consider some two dog toys such as tug rings and longer rope bones ( for other toy recommendations see the section on toys )
Enjoy you pup but don't forget the older dog.