I machine quilted a square log cabin quilt on my vintage Bernina 830 using the Bernina walking foot. This foot has a sliding guide, which was immensely helpful. I chose channel quilting with diagonal lines going in one direction,1 inch apart.
After basting, I carefully marked the first diagonal through the center of the quilt with chalk, using my 6" X 24" ruler with 45 degree markings lined up to the straight seams of the blocks. After stitching that line, I used the walking foot guide to stitch lines one inches apart. I alternated stitching lines so I would stitch on one side of the center diagonal and then move to the other. At the same time I alternated directions, so that I was stitching from left to right on one line and right to left on the adjacent line. This helps minimize distortion on the bias.
After stitching several lines, I would remove the quilt and check the straightness of my lines and used painter's tape to mark the next line. I did this because a couple of times I wandered off the straight line somehow and had to rip out a couple of rows of stitching. I think this is because I was using a domestic machine with a standard harp where it is easier to get lost.
After I had stitched the longer lines in the middle of the quilt, I began to stitch 4 or 5 lines on one side then switch over to the other side. I still turned the quilt after each row of stitching and stitched in the opposite direction.
I think this is my favorite way to quilt on a regular sewing machine. I have taught myself to FMQ, but I still get shoulder and back strain from tension and movement. The walking foot does more work for me and I don't have to fight with the quilt to SID.
Harriet Hargrave's "Heirloom Machine Quilting" has a chapter describing how to mark the central diagonal lines for channel or grid quilting on rectanglar quilts. I also liked the diagrams she showed for variations of diagonal lines.