How-to Jailbreak iOS 6.1.2:
Step 1: Update your device to iOS 6.1.2 using iTunes: if you are jailbreaking your device, why not update it to
the latest version of iOS? OTA updates might mess with the jailbreak,
therefore a fresh restore via iTunes is strongly recommended.
Step 2: Turn off Passcode Lock in case you have it enabled. In order to do this, simply head on over to Settings > General > Passcode Lock > Off.
Step 3: Download Evasi0n 1.4, which adds the support for 6.1.2 [for Windows, Mac or Linux]
Step 4: Start up Evasi0n on your computer and simply click on
the “Jailbreak” option. Kick back or grab a cup of coffee as Evasi0n
does its work and jailbreaks your device. Remember not to touch anything
while your device is being jailbroken.
Step 5: Once this is done, your device should boot straight
back. You will see a new Jailbreak icon on your home screen. Tap on it
in order to finish the process.
Step 6: Your device will now reboot quite a few times for a
short while, before it boots into the jailbroken state. Once this is
finally done, your device should boot back in a jailbroken state.
You are done: if everything has gone as expected,
Evasi0n should indicate that the jailbreak is complete. Cydia should now
also be on your home screen.