In the Oven :
This is the method we used until we got a dehydrator. Click here for a link to a website that does a great job on the steps to dry the flower petals in the oven
In the Microwave :
Here is a another article on how to dry flower petals. This one includes the process to dry them in the microwave.
Using a dehydrator :
If you have a dehydrator, here is an article on how to dry flower petals in your dehydrator.