Aly's suggestions are wonderful--we had a spoiled dog, and got another, and they fought for a while, but nothing serious, however neither were pups. My mother in law got a pom pup and her 6 year old pom was not thrilled, but they just need time apart once in a while, and the other one needs to know he is still important. Greet him first, give him treats first, feed him first-just make sure he knows how much you still love him!!