Poke a tiny hole in the center of each flower (this is where you will eventually thread the yarn through them).
Optional: Decorate the flowers with paint or markers. Also, glitter is a nice decorative touch. (Work on top of old newspapers to avoid too much of a mess.)
Cut a drinking straw into 1 1/2 inch long segments (the exact length is not important) - you'll need a segment of straw between each flower.
Cut a piece of yarn about 2 feet long. Tie a thick knot at one end of the yarn. Thread the smallest flower through the other end of the yarn -- push it down to the knot. Then thread a segment of drinking straw -- push it down to the small flower.
Continue threading flowers and straw segments. When the last flower has been threaded onto the yarn, tie the ends of the yarn together to make your necklace