Step 1. Place your pieces wrong side together. This may seem counterintuitive, but when you see how the seam works, it will make sense.
Step 2. Sew your seam 1/4 inch from the edge of the fabric.
Step 3. Trim the seam to approximately 1/8 inch.
Step 4. Set the seam by pressing it with an iron set to the appropriate setting for your fabric.
Step 5. Turn the seam so that the right sides of the fabric are now together and press the seam. The raw edge of the fabric should be in between the layers of fabric.
Step 6. Sew the seam again using a 3/8 inch seam allowance (for a 5/8 inch seam) or 1/4 inch for a 1/2 inch seam.