When I make a D9P I take a good look at not only the colour value of the fabric but at the fabric pattern. My darkest fabric is always in the centre, the most patterned fabric (ie Winnie the Pooh) which won't be sliced in the outside corners and the medium quieter print that will end up as a rectangle shape when cut in the alternate squares. This makes a good balance as I don't want Winnie the Pooh cut into tiny little bits and it will show up in the finished quilt as the biggest focus square. The small dark squares will be marching all across the quilt on the diagonal and the medium quieter print will just end up all over the place as the background. This works for me.