Don't Install It If You Haven't Prepared
If you haven't prepared your device for the Android O beta don't install the Android O beta on your Nexus 5X until you've done so.
This is early software and early software can be extremely unpredictable. If you store important data on your Nexus 5X you'll want to come into the installation as prepared as possible.
Our pre-installation process consists of several steps including making a proper backup of your key files, digging into the downgrade process, reading feedback from early adopters, and looking into potential Nexus 5X Android O problems and fixes.
This is especially important if this is your first time installing a piece of early software. Android O is exciting but blindly installing the beta could have some unintended consequences.