In an effort to give "random" a chance, I sorted my squares into piles of "bolds", "mediums" and "lights".
I then just grabbed a square from two piles and sewed them together.
I then pressed all the seams open. The next stage is laying them out (randomly) on the bed and then moving them around until I'm happy with the "randomness" of it all!
I was really impressed with myself that I realised - before I'd sewn all 144 squares together - that, on each alternate row, I'd need single squares at the ends of the row to make the pattern work. It only meant not sewing 6 pairs together but better to have realised before I sewed them together than after!