I have adopted older dogs and found this book really helpful as my first adoption was also my first. I think you would gain from it as any dog you are bringing in to foster is also your first dog.
Love Has No Age Limit: Welcoming an Adopted Dog Into Your Home
by Patricia B McConnell PH.D
It's $15 at amazon.ca
(my rescue org of choice: Oops-a-Dazy)