1. While two completely separate homes/facilities are best most of us dont have that luxury. So at the very least you need two separate rooms. One for your established critters and one for your new critters. NEVER LET NEW CRITTERS COME IN CONTACT WITH ESTABLISHED CRITTERS.
2. 90 days quarantine minimum. And while I know everyone dont practice the following, I do. Lets say you got an animal in the quarantine room for 2 months and then you bring a new animal into the quarantine room. Now every animal in there is starting over on day one. I dont know for sure what that new animal may have passed on to the ones that were already there so I take no chances.
3. Always do whatever upkeep you are going to do on your established animals first. Water changes, feedings, cleaning.... I dont care what it is. Always do your established animals before you do your quarantine animals. Get all of the work for the day done on established animals first before you mess with the quarantine animals. NEVER do quarantine animals first.
4. Always wash your hands thoroughly before AND after handling any of your animals or doing any type of upkeep with them. Particularly after working with quarantine animals. I dont care if it was just a water change. Wash your hands.
5. If you feed live never return uneaten feeders back into your rodent colony. That is just begging to spread crap all through out your collection. Either euthanize and dispose of the uneaten rodent or set up a rat rodent cage in the quarantine room just for the quarantine animals.
6. You need two of everything. I have separate paper towels, tongs, thermometers, scales, utility tubs, water dishes, hides, etc, etc, etc, for each room. All of them that are meant for the quarantine room have a big ass Q on them in magic marker so I dont get them mixed up.
I am sure I am skipping a couple of things but that right there will get you started in the right direction.