I place my pieces on my design wall then sew them together in whatever order seems right at the time. Once I get blocks done, I sew them together in either rows or columns. Usually choose whichever way is shortest. I pin wherever there are seams that need to match up. And often also where the bottom layer seam allowance will be headed back toward the needle I will pin that as well. Works best if I stitch slowly and take out the pins as I come to them.