I recommend behavioral books such as:
Nikkia Moustaki’s Your Outta Control Bird (you don’t have to have a out of control bird to want to understand behavior and prevent behavioral problems)
Barbara Heidenreich’s Parrot Problem Solver (again you don’t have to have a problem to want to learn as much as you can so you can prevent one).
Understanding their wild behavior and how birds are in captivity, and everythign BEHAVIORAL, is VERY important! This is what I would recommend, and once you have behavior down you'll understand what you need to do to improve or change your environment to better suit your birds and how to have happy birds and prevent behavioral problems.