I have been unable to find Dell's official instructions or guide for registering their laser printers to Google Cloud Print. The help pages take you in circles (http://www.dell.com/learn/us/en/04/campaigns/google-cloud-print?c=us&l=en&s=bsd suggests to look at the user manual which doesn't tell you). There is no specific section in the user guide (e.g. E515dw) explaining how to do it either.
Dell needs to add instructions on the first step for GCP which is REGISTERING THE PRINTER TO YOUR GOOGLE ACCOUNT!
Luckily I know enough on how to get to this function, but was disappointed I couldn't find the instructions online.
To get GCP working, you need to first register the printer to your Google account. To do this (which isn't documented anywhere for the E5151dw), you need to:
1. Go to http://printer-ip for example http://192.168.1.123
2. Printer displays a control panel. Select the "Network" tab (on the E515dw, otherwise find similar if you see something different).
3. Click on the "Protocol" sub-menu on the left
4. Make sure "Google Cloud Print" is checked. Then click Advanced Settings
5. Select the Register button, and continue the process - mine then said to press OK on the physical printer to continue the registration process. You will then see on the web browser to register it to your Google account (need to sign in or be signed in).
I can't believe this isn't documented online anywhere (or is so hard to find if so).