Step 1 - Download Android SDK from the developers' website and install with necessary USB drivers. - [ Register or Signin to view external links. ]

Step 2 - Download Fastboot and extract it to android-sdk-windowsplatform-tools directory. Create a new directory if it does not exist. - [ Register or Signin to view external links. ]

NOTE: Skip Steps 1, 2 and 3 if the required files are already downloaded.

Step 3 - Download SuperSU v1.04 (UPDATE-SuperSU-v1.04.zip) and copy it to the root folder on the tablet's SD card. - [ Register or Signin to view external links. ]

Step 4 - After ensuring that data is backed up on the device, power off the Nexus 7.

Step 5 - Download recovery-clockwork-touch-6.0.2.3-grouper.img and copy it to the android-sdk-windowsplatform-tools directory. - [ Register or Signin to view external links. ]

Step 6 - Now, boot into Fastboot Mode on Nexus 7. To do so, tap Volume Down and Power keys for a few seconds until some text appears on screen, which confirms entry into Bootloader Mode.

Step 7 - Navigate to android-sdk-windowsplatform-tools directory and launch Command Prompt (Shift + Right-click > Open Command Prompt).

Step 8 - Type in the following command and press Enter.

fastboot flash recovery recovery-clockwork-touch-6.0.2.3-grouper.img
Step 9 - After the command is executed, choose Recovery option from the Fastboot menu and boot the device into Recovery Mode.

Step 10 - Then navigate to Flash zip from SD card option and hit Power button to select it.

Step 11 - Tap the Power button again and click Choose zip from SD card.

Step 12 - Now, use volume keys to navigate to the UPDATE-SuperSU-v1.04.zip file copied earlier to tablet's SD card and select it with Power button. Confirm the firmware installation on next screen and the installation procedure will begin.

Step 13 - Once the firmware installation is complete, hit Go Back and reboot the tablet by tapping Reboot System Now in the recovery menu.

Nexus 7 is now rooted on official Android 4.2.2 JDQ39 Jelly Bean OTA firmware with custom CWM recovery also installed. Check for the SuperSU app in your apps list to verify if installation is successful.