Prerequisite: Nexus 7 with Android 4.1.2 build JZO54K

Manual download link: http://android.clients.google.com/packages/data/ota/google_n...

Instructions: http://www.androidpolice.com/2012/11/13/android-4-2-build-jo...

Just follow this - http://www.androidcentral.com/gsm-galaxy-nexus-android-42-up.... AC tools link has adb for Win/Mac/Linux and that is all you will need in addition to the update zip.

See: http://forum.xda-developers.com/showthread.php?t=1419170

The OTA was released this morning (I've flashed my unlocked Galaxy Nexus to 4.2).