[Verizon HTC One (M8)] drumz0rz:
I love this thread and really hope you can figure it out!

You'll need a few things to accomplish this. First you'll need to get s-off (which I explain below), then you get root access, and finally you install a custom recovery. Once that's done, you're good to go, and can install whatever custom ROM or flashy modifications you want without worry that you'll permanently ruin your phone. Here's a list of things you'll need to do it: KingRoot app, Sunshine app ($25! No way around this...), working Android Device Bridge (ADB) connection to a PC.

Note, rooting your phone (up to the custom recovery) will not erase any of your user data, however further changes (such as flashing a new ROM) likely will, so you'll want to back up everything.

s-on/off: This refers to the security setting of the phone. By default, the phone comes s-on, which protects access to reserved memory and prevents you from rooting your phone. You'll need to change this to s-off first. Once done though, it'll be s-off for good. There are ways to "return to stock" and set it back to s-on, or at least appear as such to a level 1 tech.

First thing you're going to want to do is get ADB working on your computer and ensure you can communicate with and control your phone from the ADB command line. This is arguably the hardest step for a lay person. Detailed instructions on how to get that working can be found here.

Once you can see your phone in ADB and have ensured that's working, you'll want to download the KingRoot app and Sunshine app to your phone using the sites I've linked. KingRoot will be used to get temporary root access to your phone. Once you get tempRoot, if you reboot your phone, you'll have to do it again. Temporary root access is required for Sunshine to do it's thing and set your phone to s-off. Once you have s-off you're essentially done, and the last bit of work is to install the custom recovery and then any custom ROMs or modifications you'll want.

So you have ADB working and downloaded the two apps above. Lets get started.

First, launch KingRoot on your phone, and let it do it's magic trying to get you temporary root access. It'll likely fail a few times, but just keep doing it again until it works.

Once KingRoot says you have root, run Sunshine. It'll evaluate your phone and check if it has root access. If all is well, it'll prompt you to go pay $25 for the app, and will reboot your phone.

Once the phone has rebooted, launch KingRoot again and check to see if you still have tempRoot. You'll likely need to re-run KingRoot a few times until it gets root again.

Now that you have tempRoot again, and have paid the $25, go ahead and run Sunshine again. This time, it'll know you're ready to go, so let it run and it'll set your phone to s-off and reboot when it's done.

At this point, you've broken the man's lock over your phone! Go you!

The last step is to install a custom recovery, I suggest TWRP, which will allow you to backup and restore your phone, and also install things like a custom ROM. Details of how to install TWRP can be found here. You'll be using the ADB to push the code to your phone which is why we set it up and tested it first.

Once TWRP is installed, I recommend making a backup of your phone so you don't lose any information. You can do this in TWRP.

As a final step, and a way to show off your technological prowess, you can install a custom ROM. a whole forum of options and detailed explanations on how to install them can be found here. Some retain the same look and feel you're used to, while others use different user interfaces to offer a modified experience. Review the options and feel free to ask questions!

Good luck!