I iron my seams to one side and then stick over both seam allowances. Any little wiggles in the line don't show like they do if you stay right in the ditch. In the ditch every time you wobble out you see the squiggle, next to it hides that squiggle better. But I find doing an allover crosshatch using blue painters tape to be the easiest. Just lay a line of blue tape over the whole quilt on a diagonal slant. Use the edge of the tape as your guide to stitch. Line the edge of your foot along the tape and sew all the way across. Turn the quilt and sew along the other side. Then move the tape and line it up along the sea you just sewed. Sew along again. Keep moving tape and sewing until your done. Then lay tape across in the other direction and do the same thing. Perfectly lined up crosshatches. Google "How to quilt using painter's tape" for videos.