As part of the proof reading process, put to test your email marketing campaign's call to action.
Open your email. After 3 seconds, decide if you know what to do next based on what you saw.
For example, often an email will include product information, image, and contact info in the top few inches of the email. Once the reader scrolls to the bottom, only then does the reader see the call to action, something like, "click here for more info."
Revision strategy: Move the call to action to the top portion of the email. Change the language to be more specific, "Click to view sizes and colors of our entire collection."
Remember, people do not want to open an email and have to hunt for the message. Your call to action is not an entry in a Where's Waldo contest. Write clearly, place promently.
A good article on this subject appears on the Email Critic's blog at https://emailcritic.com/2011/03/email-marketing-calls-to-action-cta/