Take a look at this Amazon email I received recently. It deploys a useful email practice, one that I've been preaching for years to retail and other ecommerce email marketers.
This email specifies all variations of pricing and discounts on the product: the original price, the percentage discount and the total money saved. What's so great about that? You make it easier for your shoppers to decide to buy from you.
This underscores a key finding in a survey of moms and their email habits and preferences, which I conducted a several years ago. Moms, especially those with young children, have many demands on their time and don't want to pull out a calculator to figure out whether a 20% discount will save more money than a $10 price cut.
Other customers might have different motivations. Some will be attracted to a sizable percentage off, while others will act by seeing how much money they save or contrasting the original and discounted prices.
Doing the math for your customers is a start, but "make it easy" should be your email mantra every time you send an email. Every aspect of your email message - from layout to navigation and content - should help your customers decide to buy or act.