when I fix antique quilts I trim the old patch away measure the new patch so it will fit into the space very carefully with tiny stitches sew the patch onto the space making sure there are no bubbles or uneven fabric try to make it so the stitches do not show. iron the patch to make sure it fits into the space. try to use a fabric that goes along with the quilt top so it looks natural and if there is any splitting of the fabric beside the patch be sure to tack those down so they don't spread.