The following instructions assumes you already have your internet set up and working with CenturyLink. This is not for CenturyLink fiber setups. The modem I'm using is the ZyXEL C3000Z which was provided by CenturyLink.
To start, connect the dsl port on the Modem/router CenturyLink device (will call it "modem") to the wall phone jack and then plug in the power cable. Also connect the Google WiFi to power. Do not connect the two devices via ethernet yet.
Once they are both powered on, factory reset both devices. I've found this will cut down the number of problems during setup.
Reset Google Wifi: If you've previously set up a network with this device you'll need to reset the device through the Google WiFi app to get it to be removed from your list of owned networks. To do that go to the settings page (gears icon on right side), select "Network & General", select "Wifi point", and click "Factory reset." You can reset only the device by pressing and holding the button on the back the de