1.Download the Android 4.2 Launcher apk file and transfer it to a convenient location on your phone.
2.If you are using a Nexus Device or running an AOSP /AOKP based stock Android ROM, you need to be rooted. Download Titanium Backup and uninstall your default Android 4.1 launcher. If you are using an OEM customized ROM, like a Touchwiz based or HTC Sense Based ROM, you can skip Step 2 and move on directly to Step 3.
3.Now using a File explorer like ES File Explorer or Astro, navigate to the location where you had transferred the APK file for the Android 4.2 launcher, in Step 1.
4.Install the Launcher apk, and enjoy the default launcher from the upcoming Android 4.2