MIUI 8 Global Developer ROM is now available on most Mi devices and can be easily flashed either via fastboot or Mi recovery. If your device is among the supported devices to first receive MIUI 8, you can follow the guide explained in this post to flash the downloaded ROM via fastboot or via recovery.
Note that this guide can also be used to flash any MIUI ROM that contains fastboot flash-able files.
How To Flash MIUI 8 Via Fastboot
Step One: Download Mi Flash Tool from the link above. Unpack and run the installer.
Step Two: Power off the device and reboot to fastboot mode. Can be easily done by pressing Power button and Volume Down at the same time.
Step Three: Connect the device to your computer now without pressing any button
Step Four: Unpack / Decompress the download ROM package to any folder on your Computer and copy the folder path.
Step Five: Now launch Mi Flash Tool and paste the copied folder path in the space provided to browse for ROM path. See screenshot below..
Step Six: Click on Refresh button to detect your phone. Then click Flash to commence firmware flashing.
Step Seven: Wait for some time for the flashing process to complete. Once complete your device should reboot automatically to MIUI 8. Done!
If you have any questions or complain please post in comments section below.