Have Your Info Ready
Ordering an iPhone 8 or iPhone 8 Plus will require more than just your credit card number. You'll need to have some very specific information on hand.
At the very least you'll need to have your Apple ID and carrier login information ready. That includes the user name and password.
If you aren't the primary account holder, make sure you get that information ahead of time. Make sure you have your Social Security Number (or the account holder's SSN), and the account billing information handy.
Some carriers might require you to ship the device to the primary billing address so if that's not your current shipping address, you'll want to address that.