Well-written Metro style app code that doesn't include implicit or explicit dependencies on platform architecture can be executed on Windows RT PCs. The existing documentation in the Windows Dev Center about how to design and develop Metro style apps for Windows 8 provides adequate guidance for most of the basic scenarios and questions you will have. However, the Windows Dev Center documentation doesn't include certain information that pertains specifically to Windows RT characteristics and scenarios. This document offers such Windows RT-specific information.
Also, this document includes links to high-level entry points into the existing Windows Dev Center documentation. These links are useful if you're just starting out with Metro style app development.