I recently made a 'diamond' quilt that I quilted on the diagonal using a ruler. I wanted to use my quilting foot because I had to go around some applique but soon found that I can't sew a straight line to save my soul with the quilting foot. So, I took my "Add a quarter" ruler and placed painter's tape on the under side to show the width of the rows I wanted. By using the thicker side as a guide, I just placed it so the previous stitching line and stitched with the foot right against the edge of the ruler. It worked great! I put some photos up, here's the link.
http://tjzoriginalz.blogspot.com/201...-now-what.html
http://2.bp.blogspot.com/-dJklyfYY5b...uilt%2B001.jpg