Summarize this article:

If you intend to dry sunflowers for decorative purposes, it is better to use small- to medium-sized sunflowers that have only just begun to open. The seeds have not fully developed, so they should not fall out after being dried. The stem should be about 6 inches (15 centimetres) in length, so cut your flower accordingly. Pick a pretty, symmetrical bloom, and pull off any dead leaves around the head of the sunflower. Tie yarn or kitchen twine to the bottom of the stem. You can bundle them in threes, but the heads shouldn't touch. Pick a dark, dry place to hang them, such as an unused cabinet, a closet, or an attic. You can also set the flowers in a vase to dry. The petals will arch more gracefully. Still place them in a dark, dry place. The sunflowers should be dry in about two weeks, but they may take as long as three weeks. When they're dry, cut down the twine and pull them out of the closet. Preserve the color and shape of the flower by spraying it with hairspray. Use them in vases or cut the stems short to place them in shadow boxes.

Summary:
Harvest partially open sunflowers. Cut your flower with a decent-sized stem. Hang the sunflower up to dry in a dark, dry place. Check on the flowers in two weeks. Coat the sunflowers with hairspray.