The Windows 8 app developer blog recently published How to improve performance in your Metro style app. A lot of the content might be familiar, including the always-handy Interaction class table, but there are additional considerations to play nice with the rest of the system, particularly with regards to how expectations change for different app states, so I recommend reading the full thing.

And if this whets your appetite, you can always learn more at the Windows Performance Analysis Developer Center.

Enjoy!