I grew up in a house with dried flowers and I taught myself different methods to press flowers when I was an adult. I don't pick flowers but it is easy enough to find great looking flower heads on the ground in San Diego. Once this was pressed I sealed it to the page with a bit of liquid gloss medium.
The trick is to press the flowers right away so they retain their color. If you are in a hurry you can use the oven on the lowest setting. I plan on pressing some of the lovely clover that is popping up all over the city. With all the rain they are triple the size this year. No luck finding a giant 4 leaf clover.