One way to do this is with Website Optimizer, a free Google tool that allows you to compare multiple versions of a Web page and statistically determine the version that performs best. For instance, Kelly explains, you can create two different landing pages, one with four small pictures versus a page with one large picture, and "scientifically determine" the design that has the highest conversion rate. "Sometimes small changes, like changing the size of an image or the wording of a special promotion, can improve conversion rates by 10, 20, or even 50%," she writes.