Choose your embroidered iron-on trim, which typically comes on a roll and is purchased by the yard. Use a pair of detail scissors to carefully cut into the trim.
On a flat surface, piece together your desired design. For the most durable necklaces, make sure the applique pieces overlap one another.
On another flat surface, lay out a piece of fabric, cut slightly larger than the design. (The fabric layer will back your applique and ensure that your necklace is sturdy.) Cut a piece of cord or ribbon to the desired necklace length. Drape it on the fabric. Transfer the design onto the fabric, sandwiching the cord.
Iron all layers to seal. Let cool. Use detail scissors to cut away any excess fabric.
Trim the ribbon to the desired length, and knot the loose ends to finish.