1. Simply download clockwork recovery image. (click here)
2. Reboot into boot loader / fast boot mode
(Volume Up + Power)
3. install clockwork recovery image
4. Boot into Clockwork recovery and install Superuser from Market (QR code provided)
If facing any problems i.e. unable to access root, not able to gain proper file permission when in recovery mode / boot loader. Click here for more details and guidelines.