Every page on a website should have a call to action. In other words, what do you want the visitor to do when they arrive on that page?
It could be as simple as wanting them to phone you - in this case, don't hide the phone number away in the footer, place it somewhere prominent. It’s not a call to action if your visitor has to look for it.
Ideally, a page should just have the one COA and be designed specifically to encourage that action. So for example, if you’re looking to encourage people to sign up to your newsletter, make sure you give them plenty of reasons why they should, and place the sign-up form where it can’t be missed.