Here is a great post to get your started on managing multiple dogs
Disciplining the dogs through feeding on All things dog blog is a must read especially if you are a dog foster parent and have new dogs coming into an existing stable house and leaving.
It is really important to establish the humans in the house as pack leader to avoid fights and general instability and inconsistencies. Your existing pets also have to go through the cycle of change, with every new foster dog, and making some rules and sticking to them makes it easy on both you and the dogs in the household.
Check the above links out for some great tips!