This is what I think of when I make placemats. Lots of patterns feature a central design, but when you think about it, your plate covers this up. I generally try to find a side design, so that when the plate is on and you're eating, you can still see the design. I have made A LOT of placemats, and one of my favorite design is to make a strip pieced inset off to one side, add some piping or a little flange on either side to coordinate with the fabric.