Create Urgency In Call-To-Action
Compelling your email audience to click the "BUY NOW" button isn't enough. You have to make them WANT to buy by creating urgency. I.E. instead of saying "Order now for delivery by Christmas" say "If Santa can deliver in a day, so can we!" It puts whimsy and comedy in your point while making the statement relative to the message, thus making the reader take action!