In the past, direct marketing was done through mail. A flyer would be embedded in your daily bundle of letters and bills, and more often than not, would find itself in the trash can before long. Nowadays, a lot of marketing is done through email. As a business owner, you want to sell your online gift cards, but you do not want to end up in the virtual trash bin. We have found an infographic (courtesy of marketingprofs.com) that we feel accurately sums up what needs to be done in order to ensure that your customers are reading your emails.
In short, use capital letters (when appropriate) in your subject, keep details in the subject on an essential basis, and really try to cater to your customers through personalization and attention-grabbing visuals. If you create promotions that stand out visually and appeal to the demographic of your consumer base, they will respond with their business.