My Lady was tied to a tree and left behind by her previous owner when she moved. That was eight years ago and if you could see her now, prancing around in her beautiful dresses and bows, you would never believe it!
Adopting an adult dog is very different than getting a new puppy, but there are also a lot of similarities. In many areas, like housetraining, you have to go back to basics and treat them exactly as you would a puppy. You have to always remember that unlike puppies who love you almost instantly, you often have to first earn trust, and then love, with an adult dog. Once you have earned that love, though, you will never feel so rewarded and loved in your life.
A fabulous book that helped me and is recommended by many rescue groups is
Secondhand Dog by Carol Lee Benjamin. Amazon has it or you can have your bookstore order it. It's very inexpensive, under $10.