There are often posting about the 1/4" seam in quilt making. The following was posted on another site. I felt it was so good that I wrote the writer and got permission to post it here. It was written by Lyn D Johnson on one of the sewing machine sites.
"You are the craftsman and operator, your sewing machine is equipment and your quarter inch foot is a tool. The equipment and tool require the skills of an operator, or they will do nothing.
Everyone feeds fabric into a machine with different variance at the edge of a foot or guide. It is worth the time to work with your machine to perfect your quarter inch seam. The few minutes it takes to train yourself on your machine (and each machine and foot is different) reduces your time in ripping seams, resewing seams, and trying to fudge seams to match.
Try this test: cut four rectangles 2" x 3.5". Place two rectangles right sides together. Making certain that the edges are matching exactly, sew a quarter inch seam along a long edge. Press the seams (I prefer open, first from the back then from the front), making sure there are no pleats or fullness in the seam. This square should measure exactly 3.5 inches. Repeat for the other two rectangles. Place squares right sides together with one seam horizontal and the other vertical. They should fit together perfectly. Join the two squares as you would quilt squares.
If they do not fit together perfectly, or if they do not measure 3.5 inches, determine whether your seam needs to be smaller or larger. Use the guides on the bobbin cover to help you guide your fabric into your quarter inch foot.
Precision piecing will save you so much time as you make more quilts. If you are interested in precision piecing, I recommend Sally Collin's The Art of Machine Piecing. She gives great tips to improve your quilting skills."