1. Place fabric, wrong sides together.
2. Sew fabrics together.
3. Iron or finger press seam open.
4. Trim one seam to 1/4" its original width.
5. Fold the longer edge over the shorter trimmed edge. Iron.
6. Sew seam close to folded edge.
7. Finish seam by stitching a second seam, catching outside folded edge.
This is a great way to sew a "patch work" fabric to use for blankets, bags,...