ideas that have helped various mutts at out place settle in -
Give them some old clothes (shirt, blouse, etc of the one it spends most of it's time with as bedding.
Does it have a favorite toy? If not go to Petco, take the dog and let it pick one out.
last choice would be a wee drop of Valium on its breakfast. I hate that choice but had to use it one time but after about 4-5 days it was no longer needed.