As coupons are good only for limited periods of time, you should develop a habit of searching for them before each and every online purchase you intend to make.
Sometimes, you may apply such coupons codes in brick and mortar stores, so you can save them in your phone, and show them to the shop assistants. Many store chains use this method to attract more people into their physical stores.
They know the psychology of the average buyer very well, so they are willing to offer discounts on some products to attract buyers into checking out their stores. Once there, most people wouldn’t be able to limit their shopping to the products they had in mind when they decided to get there.