I came up with this process of creating a random quilt back when I was trying to use only scraps on the back of my World of Goo quilt. I simply sewed strips of larger scraps together. Then I would cut the quilt back in two pieces, rotate the pieces and sew them back together, sometimes adding more pieced scrap strips in between. I took pictures after several steps in my process of creating my quilt back for A Day at the Aquarium to show how it changes.
I started out with four colors pieced the width of fabric.
I sliced it into two pieces, rotated one piece, and placed another strip in between. I continue to even out the edges of the quilt as I go.
I did this same step, again adding another strip in between.
I added one more vertical strip then started the process horizontally. I cut the quilt into about 5 pieces horizontally and flipped them around before sewing everything back together.
I continue cutting, rotating and adding new pieced strips until I'm happy with the result. It's a simple way to get a fun, random quilt back without too much thinking or work. It's also a great way to use up all those scraps because you can piece you strips any width, you can use the smaller scraps as well.