How to Install Cyanogenmod on an LG G2 D800

CyanogenMod is an open-source operating system for smartphones and tablets, based on Android. It offers many extra features such as support for theming and lossless audio, Privacy Guard, and built-in support for tethering. Unfortunately,...

Part 1 of 3:

Root Your Device

Plug in your phone to your computer via USB. A prompt may pop up on your Android device asking what mode you'd like to use to connect. Select Media Sync.
Ensure that the USB drivers install correctly. You may find later that you need to download them manually from the Internet.
Download the latest version of ioroot and extract the zip to a folder.
Unplug your phone from your computer and ensure that Developer Mode is enabled. If you do not see a "Developer Options" option in your settings, you need to enable it. Go to Settings > About phone and tap on "Build number" seven times. You will see the message "You are now a developer!"
Go to Settings > Developer Options and check USB Debugging (you won't be able to change the setting if your phone is plugged in to your computer).
Reconnect the phone to your computer. Open the folder you previously extracted ioroot to and run the ioroot.bat file. Follow the instructions shown to root your phone. It will ask you to disconnect your phone and disable USB debugging and then re-enable and reconnect. Be sure to continue with the root when warned of warranty voiding -- you can always unroot later. If the tool does not detect your phone, you may need to try different drivers.
Confirm that you have gained root access on your phone. The easiest way to do this is using the Root Checker app in the Google Play Store. If you have not gained root, you may need to try a different version of ioroot.

Part 2 of 3:

Install a Custom Recovery

Do not use TeamWin Recovery Project (TWRP) as a custom recovery. You will see guides for TWRP and LG G2 online -- these are for other models. TWRP uses an exploit that has been patched in the D800 Android firmware. If you try to flash CyanogenMod using TWRP, you will soft-brick your phone and will need to restore it to stock Android and start the process from the beginning.
Download the ClockworkMod ROM.
In ClockworkMod Recovery, use the physical volume buttons to move up and down. On most devices, the power button is used to confirm a menu selection.

Part 3 of 3:

Flash CyanogenMod

Download the stable version of CyanogenMod for the D800. You can upgrade to the snapshot or nightly later once you have successfully installed it.
Boot into Recovery Mode and connect the phone to your computer.
With the device powered down, hold Volume Down & Power. When the LG logo appears release the buttons and then press them again. Then, press the Power button three times.
If you skip this or any of the next three steps, CyanogenMod will likely get stuck in a boot loop, and you may have to re-flash CyanogenMod or even restore from stock and start from the beginning. In ClockworkMod Recovery, use the volume buttons to scroll down to "wipe data/factory reset".
Scroll down to "wipe cache partition" and select "Yes - Wipe Cache".
Scroll down to "advanced" and select "wipe dalvik cache". Select "Yes - Wipe Dalvik Cache". Press Go Back to go back to the main screen.
Select "install zip"
Use ADB to push the CyanogenMod ROM file to your /sdcard directory (yes, this directory exists even if you don't have an SD card). You will need to do this while in normal mode, as ADB may not detect the device while it is in Recovery Mode.
Select the zip file from /sdcard/0. Wait for the process to finish.
Reboot and enjoy!