I always make sure the Oldest maintains their status as the Leader of the pack......in that way, the older dog will contribute to the training of the new pup. So the oldest is always first in the house, first out of the house, first one i greet when i come in, first to get food, first to get treats, etc.
I always show deference to the oldest...and also very important that the possessions, treats, bones, toys , bedding are respected by the youngest addition. Teaching the pup, to respect the elder dog's status is KEY in them getting along in the future.... it is non- negotiable in my home.