Step 4: Miter, Baby!
Using a generous 1/4-inch seam allowance, stitch the first side together. Stop 1/4-inch from the first edge you reach and backstitch two stitches or so.
Take pot holder off sewing machine, and fold it for mitered corners as shown. First, fold strip up, then back down along the adjacent side raw edge. This will leave a triangular fold where you will resume stitching.