This is the Android device configuration for Xperia Z
To setup a tree and build images for the device do the following:
To flash the images produced make sure your device is unlocked, as described on http://unlockbootloader.sonymobile.com/
Enter fastboot mode on the device by pressing volume up while inserting the USB cable or execute adb reboot bootloader.
Reflashing userdata is not necessary every time, but incompatibilities with previous content might result in a device that doesn't boot. If this happens try to reflash just the userdata again.