Encourage customer to buy more of your product impulsively. Intercept them before they pay for the final price. Just like when they put candy and bubble gum at the front of cashier counter in every convenient store.
When it comes to eCommerce, Amazon.com adapts this technique really well. When users click for more info about a book, they would find details, reviews, and related products. Plus, they offer them special price if they buy that related product along with the first book.
Not only book, let’s take example of other kind of product. Say electronics. When your online shoppers decide to buy a digital mp3 player, at some point offer them to also buy some screen protector, mobile charger, or other peripheral. They may want those extra item but may forget or don’t know if such item available in your site.
Other technique is to give limited time offer. Sounds so common but this actually works well. People likes taking advantage no matter how small they can get. Give them special offer that valid “Only 3 days left”, and most of them will break. But every time you make limited time offer, be serious. Lay off the offer when the time expires. Otherwise, you’ll lose credibility.