Bichon/smaller dog owners need advice regarding another dog..

I have a 1.5 year old Bichon Frise who is our little boy. For a month we dog sat for my father in law with his 5 month old English pointer-beagle mix. Great dog, but it was a nightmare for our 2 cars and our Bichon. She wanted to be the dominate one and was just too much for our animals. Tomorrow we are going to go look at an 8 week old pom-pug mix and probably will want to get him. What helps getting animals to become friends and get along better? I've heard seperating them for a few days helps, but we are hoping since it is also a smaller dog everything will go smoother than with the one we took care of. He has gotten along well with dogs in the past and gets along great with the cats, we just want to welcome another pet in our home and everything go smoothly.