A lot of the Metro design principles – such as content over chrome, pride in craftsmanship, and using typography for content hierarchy – accrue to having great alignment in your application. Ensure you pay attention to alignment and follow the recommended margins in Windows 8.
The design assets for Metro style apps are a good reference for your base layout. Leveraging the Visual Studio templates for Metro style apps is also an easy way to jumpstart your app to a good layout.

Reference (HTML)

http://msdn.microsoft.com/en-us/library/windows/apps/hh465386

Reference (XAML)

http://msdn.microsoft.com/en-us/library/windows/apps/hh465386