We posted some simplified instructions for installing the Android M Developer preview to your Nexus device yesterday, but there is an even easier way to install the Android M Developer Preview! If you have ever rooted your Nexus device chances are you have heard of the Wugfresh Nexus Root Toolkit. This is a toolkit that makes it incredibly easy to do things like unlock the bootloader, root the device, and even flash stock images. The ability to flash stock images is what will make flashing Android M super easy!
Grab the appropriate file from Google at the link below. Grab the Wugfresh Nexus Root Toolkit. Chose the option to flash the stock image and unroot. When it ask which version you would like to flash chose your own. Also be sure to enable the force flash mode when it ask. This is currently available for Nexus 5, Nexus 6, Nexus 9 and Nexus Player.
Download M Image
Wugfresh NRT