I do something similar to Prism but carry it one step further. Once you have put the sashing between the blocks and are ready to put the long pieces between the rows, Take your ruler and mark where each block seam starts and ends on BOTH top and bottom of the sashing. Eg: your first mark would be at 10 inches (block minus 1 seam allowance), then the width of the sashing between the blocks, then 9 3/4 inches, then the sashing etc. Now you have a reference for every block and they should line up perfectly. Alternately, you could use cornerstones, which would keep the blocks perfectly in line too.
Strips cut across the width of the fabric have a little more 'give' than strips cut from the length of the fabric. That's really the only difference.
Last edited by GingerK; 02-17-2015 at 05:21 AM.