Google released the first developer preview for Android O today, and many users may be looking to flash it onto their compatible device. Well here's how to do it. It's actually quite simple, and since the Android Beta Program isn't yet set up for Android O (it should be within the next few days), the only way to get Android O is by flashing the entire factory image. Google is supporting the Nexus 5X, Nexus 6P, Nexus Player, Pixel, Pixel C and Pixel XL with this developer preview. First off, you'll need to have your bootloader unlocked, before you can flash the factory image onto your device.
You'll need to get a USB-C cable and plug it into your device and into your computer before you get started. You'll need to get into fastboot mode, and then open a command prompt window on your computer. In there you'll need to type ./fastboot devices. From there you should see your device appear. If you do, then you're all set and ready to move on. Now you'll need to type the command ./fastboot flash bootloader [bootloader-file-name]img. Once the bootloader has been flashed, type in ./fastboot reboot bootloader. Next, you'll type in ./fastboot flash radio [radio-file-name].img and followed by the ./fastboot reboot bootloader command. Now the next command will clear the data on your device, which isn't needed but is definitely recommended. Use the command ./fastboot -w update [image-file-name].zip.
After you've done all of that, you should be all set to reboot your device. Now keep in mind that it will take some time for the device to reboot. This is common after updating to a new version of Android, as the cache needs to be rebuilt and everything put into place before it finishes booting up. So if it takes longer than normal to boot up, don't worry too much. You can download the factory images from the link below. Be sure that you download the appropriate image for your device, or you could end up bricking your smartphone, which is something that you definitely don't want to do or deal with.