VS2012 Update 1 is great it adds the Microsoft Fakes framework for stubbing out SharePoint dependencies and other really useful tools for SharePoint development. If you’re using Visual Studio 2012 you should be using Update 1; but it doesn’t have the extensions for 2013 development as yet. To get those they need to be installed using the web platform installer.
1) Download and install http://www.microsoft.com/web/downloads/platform.aspx (you should probably do this for all development environments anyway)
2) Launch the Web Platform Installer and search for SharePoint
3) Add install the latest version of the “”Microsoft Office Developer Tools for Visual Studio 2012” (currently it’s Preview 2)