Once the piece is totally sewn you can decorate this by stitching on the cord or ribbon. This should be done with a couching stitch. This will also hide all the whipstitching giving a nicely finished look.
If using ribbon or a flat trim, sewing in place is not necessary. Simply pin it in place with your glass pins. If you want a bow or loop with the cord, you must plan the length needed for it as you stitch the cording in place. Be sure to secure the end of the trim if needed by placing a drop of glue on the start and finish to ensure it does not ravel. Wait for the glue to dry before pinning.
Start pinning by placing the first pin in the corner (allow the trim to start exactly in the upper center which will be hidden by a bow later). The second pin is placed in the center of the side than a third on the next corner and you continue this around the pinkeep.
Couching stitch diagram: http://www.medievalwardrobe.com/item/48
Once you have pinned around the pinkeep, go back and place a pin between the corner and center pin all the way around the pinkeep. See photo above for placement. Cut the trim to size and place a drop of glue to the end once again and press in place. This should be given time to dry. If using ribbon, you can simply allow the edges to overlap by a fraction and it will be ready for the next stop. There is no need to glue.
If using cord, once you have couch stitch this in place, your cord will be then tied into a small bow which can then be unraveled slightly to give the look of a tassel. For cording, no glueing is necessary.