Hey, congratulations on making it to the AT! As to preparation techniques, I think there are loads of people here who are more qualified to answer your question, as they have been through the actual thing. My two cents is rather generic; just make sure you have a good nights' sleep before the day of, and keep cool while you are doing the test. You can find some more good hints for the AT within this thread. If you are rather rusty on your coordination, you can play some MS Flight Sim and try landing a C172 in a 30kt crosswind!
Not sure about the dresscode, I'd wear a business suit but perhaps some other people who have done the AT can fill you in. I'm quite positive there won't be any surprise interview after the AT though.
Best of luck!