I was taught by a quilting teacher to buy the thick "mole skin" pad that is found in the Dr. Scholl's area of your local store. It comes in a rectangle that's about 1 and1/2" x 3". It is sticky on one side. Cut out a strip along the 1&1/2" side that's about a 1/4" wide. I use a ruler and my rotary cutter to get a straight, clean cut. This gives you a small "wall" to lay down on your scant quarter inch line from your foot toward you on your machine. Then, when you are piecing, just line the edge of your fabric with that edge while you are sewing. The thickness of the "skin" makes it so that your fabric stays inside that line. I hope this is making sense to you. It works really well, and when your skin starts to wear out, you can pull it off. You will have plenty of extra to keep cutting more pieces.
OOPS! Just realized that the reply above said the same thing! Sorry for the repetition!