Choose flowers that have thin petals, like zinnias, rather than fleshy ones, like lilies. The flowers will dry faster with less chance of rotting and turning brown.
Select flowers that have small blossoms like larkspur or flat flowers like zinnias, with the exception that roses dry well when nearly fully opened.
Keep the flowers in water as you prepare them for pressing. Wilted flowers will look wilted after they've been pressed.
Remove the stem from the flower as close to the end of the bud as possible. Remove any leaves as well.
Place the flowers face down on white paper that has been inserted into a phone book. Place a few sheets of white paper on top of the flowers. Close the phone books so 50 or so pages are between the first group of flowers and the second. Repeat the process with the second group of flowers arranging them so the new flowers are not right above the first layer of flowers.
Put the phone books in a warm dry place. Weight the phone books with the flowers with additional books or weights on top. The flowers should be completely dry and pressed within two to three weeks.