Windows 8 RTM is now available to developers along with the RTM version of Visual Studio 2012 and the Windows 8.0 SDK.
Developers working on games for Windows are already familiar with the DirectX SDK. Important changes to the DirectX family of technologies are included in the new Windows SDK, which is the new home for the DirectX SDK. Be sure to read “Where is the DirectX SDK?” for the details.
Windows 8.1: Note that these guidelines also apply for Win32 Desktop games running on Windows 8.1. The Windows and Windows Server compatibility cookbook has been updated with notes about Windows 8.1. Pay particular attention to the OS version detection behavior change, as well as the new 200% high-DPI scaling mode. Also note that in Windows 8.1 DirectPlay is now a distinct Windows feature that is off by default.
With a new release of Windows, publishers and developers want to ensure customers running Windows 8.x continue to have a great experience running their current catalog of games for Windows 7. Developers interested in Windows 8.x software certification program should be sure to read the latest version of those requirements, which can also allow you to have your Desktop application listed in the Windows Store. The older Games for Windows Technical Requirements and Test Requirements documents are still applicable best practices for desktop Win32 games on Windows 8.x. There are some additional things to keep in mind when your game is run on a Windows 8.x machine.
In addition to the existing Windows 7 best practices, you should review the Windows 8 and Windows Server 2012 Compatibility Cookbook for detailed application compatibility notes on various Windows technologies. In particular, you should review the topics
In addition to learning about the new Windows Store app model (a.k.a. Metro style apps), here are some important things to consider when creating Windows game titles for Windows 7 and for the desktop of Windows 8.
Update: This page has been updated on October 25, 2012 for Windows 8 GA (was originally written for Windows 8 Consumer Preview).
Related: Dual-use Coding Techniques for Games, DirectX SDKs of a certain age