You can make tons more money just by getting your customers to slightly increase their orders. Learn from Amazon, it earned a 35% increase in profits in 2006 by using these two tactics. It makes the most out of the frequently bought together and customers will view these items, also suggestions. But how to implement?
One way is that offer the same print on demand designs in several different fabrics and in more premium versions. You could use testimonials and reviews to show how it is worth by adding just a few dollars to get a much better product.
For cross-selling, show customers add ons that are complementary, but at least 50% cheaper than the main item of interest. But remember, don’t push the entire category of your store, or else your customers may get confused and add nothing. Get the complimentary recommendation focused.