From Deb (USA)

Flat drying can be done by placing flowers inside a folded paper towel or a piece of wax paper. Put inside a heavy book for about two weeks. Leave a little piece of the paper towel or wax paper hanging out of the edge of the book. That way you can find it more easily. This method will flatten your flower, but flattened flowers may be excellent to use as a decoration to frame mats, picture albums, hand made cards, or even make pictures from dried flat flowers. Directions:

Air-drying can done simply by using string or twine to hang flowers upside down in a warm dry place out of direct sunlight. Make sure to cut away all dead flowers and leaves that you would not want to use before drying. In about one to two weeks, flowers should be dried enough to break easily from stem. If flowers are to be used as a decoration, for example roses, you can spray them with hair spray or clear acrylic enamel to preserve them better. However it would not be good to spray flowers that are to be used for potpourri. The chemical smell from a spray would overpower the natural scent of flowers.

Another way of air drying flowers would be to use a wooden framed box with a screen or cheesecloth bottom. Place a single layer of flowers in box, making sure air is able to circulate. Gently stir or turn flowers every few days. Flowers should be dried in about a week.

If you wish your flowers to keep their shape when drying them, you can use Silica gel crystals, which you can buy at craft or garden stores. Follow directions on container.