Be prepared!

To me, this is basic - something we should have learned in school.  Being prepared is so important, especially if you're calling to order something, or to put in an application for something.  Places that take phone orders or applications are often swamped, so it's very important that you have the information they need.  Obviously things like your name, address and phone number are easy - but depending on what you're ordering or applying for, you may need to provide your social security number or credit card information, so if you don't know that information off the top of your head, be sure you've got it ready when you call.