Put your ballet shoe on and tie any elastic string around the top of the shoe. Place the strap over the top of your foot between the arch of your foot and your ankle. Pull the strap until it is tight. Mark a line on each side of the shoe where you will attach the strap. Mark a line on the sides of the strap where you will sew them to the shoe.
Cut the strap with the scissors. Cut 2 inches below the marks on each side of the strap. Remove the shoe. Pin the strap to the shoe with the safety pins where you marked the lines. Turn the heel of the shoe inside out.
Thread the needle and tie a knot at the end of the thread. Insert the needle on the inside edge of the shoe. Push the needle through the shoe lining and one end of the strap. Stitch a zigzag pattern to attach the strap to the lining. Stitch a line over the zigzag stitches to secure them. Knot the thread and cut it.
Sew the other end of the strap to the shoe. Try the shoe on and confirm that it feels comfortable. Trim the ends of the straps below the stitches. Sew a strap on the other shoe.