This is the same technique that we used in making rag rugs. These are my own figures so use what you like.
l. Determine the width of quilt you want minus the borders. Have at least three coordinating colors, light, med and dark always work.
2. Take the number from the width and then take 34 %, 55 % and 83% of that number. Cut your strips in those lengths.
for example lets say you want a 60 inch wide (without the borders) (and ignore the seam allowance and the part that you lose when sewing it together). So 60 times .34 is 20.4. ......and 60 times .55 is 33 .....and 60 times 49.8.
And I would cut my strips in 20 1/2, and then 33 and then 50 inch lengths.
You need some 20 1/2 in each of the colors so you would end up with 9 piles of strips. Lay them in stacks around a table and go along and pick one from each stack and make your pile to sew. Arrange the strips so that the next pile is not the same color or size.
This gives a total random look.