Harvest the fresh leaves just before the flowers begin to bloom. Look for stems with tight flower buds that haven't opened yet. Place them a basket or bowl.
Lay the leaves on a drying screen, being careful not to overlap or stack the plant material. This will help the leaves dry evenly. If you don't have a drying screen, using a cookie sheet or even a piece of newspaper will do.
Place the drying screen in an area that is warm and airy. Arranging the drying screen in a quiet, sunny room near an open heater vent would work well.
Turn the leaves occasionally if they are not laid out on a screen where air can reach both sides. Drying the material as quickly as possible will prevent molding which will damage the final result.
Test the dry leaves by gently bending; if they feel slightly brittle to the touch, they are dry enough to be stored. If they still feel slightly limp or leathery, let them sit awhile longer.
Store the leaves or flowers in an airtight container.