**TIP** When adding the sashing pieces, attach to the same side piece of block or row each time so that on the backside, the stitching (and flap) will be on the same side. If I can figure out how to post a pic I will try to make this more clear (if anyone doesn't understand what I'm trying to say).
This will also be clear if you plan the attaching step so that your new block or row is always to the right of your foot (not the bulky part of the quilt). This will become apparent as you add more and more rows.