You're going to want a thin cloth to dry the flower with, and a thick book. Get a couple of pieces of paper to protect the book's pages from colour that might come off of the petals, then press the flower in between the middle of the pages.

[That can take a while, though, so she adds:]

If you want to press it a little faster, you can put a weight on the book - a rock will do. Once it's dry and pressed, you can mount it and put a picture frame around it. I recommend pressing a few flowers together in an arrangement.