Jailbreak Apple iOS 4.2.1 for iPhone and iPod Touch [All Devices] using Redsn0w 0.9.6b3

The Apple iOS 4.2.1 was released this week (currently in GM)  for all the compatible devices including iPhone 4, 3GS, 3G, iPad and iPod Touch. The new firmware 4.2.1 can now be jailbroken using Redsn0w 0.9.6b3 that is available for both Windows and Mac. Follow the guide below to proceed with the jailbreak.