Use a small fine brush to completely cover the flower petals
Sprinkle the flower with superfine granulated sugar (found in the baking section of your store)
NOTE: The sugar can be colored to match the flower by mixing in a little petal dusting powder.
Shake off the excess sugar and dry the flowers completely. Small ones can be left to dry on power towels. Larger flowers, such as roses, wrap a piece of wire around the stem, and dry hanging upside down from a glass or other suitable item to avoid squashing the petals.