Look at the decorative stitches on your machine. I use what is called the serpentine stitch at the widest width and a length of 3 or 4. I stitch on top of each seam and don't worry if it is straight on the seam. The curves offset the straight seams. Quilting on the seams at the 2 inch intervals makes a nice rippling texture. The serpentine stitch is like a huge zigzag but has rounded points.
Serpentine stitch is a GREAT stitch to use one just about anything!