I would enlarge the illustration to take up a lot more room on the shirt so customers can see it easier on cell phone thumbnails.
If possible, avoid using Zazzle’s auto-generated mock-up images. Make your own cover photos, so your thumbnail will stand out against all the other motivational shirts that are using the same mock-up image.
Most of the motivational shirts on the first page of the popular feed are not customizable. So, add some additional customizable text so you’re offering something different than most other designers.
There are 214,000 motivational shirts in the Zazzle marketplace. All of the shirts on the first page of search results are very generic. So make your design more specific, like “Be the Best Dad You Can Be,” or the best baseball player, or the best teacher, etc. You get the idea.
Your work will be easier to find if it is targeted to a specific group of customers. Hope this helps.
