If I had a "best-seller", it would be my quotation patches. They're small and can be stitched on anything.
Wanting to do something different, I experimented with a larger piece. I drew a group of cat faces (cats' chorus?), and transferred the image onto a large piece of cotton fabric. I liked the result, and it's now a new listing in my Etsy shop.
Simplicity is the removal of the useless and the unnecessary--source unknown