Start my cleaning the mirror with soap and water to remove any debris or dirt, and let dry.
Choose a paper doily that works for the size mirror you have. My doily is about a third of the size of mirror. On the backside of the doily, place double sided tape all over.
You will want to overload it with tape so that you can stop the spray from going into areas you don't want it to be. But you also want to be sure not to put tape over any areas that are suppose to be "open" in the doily. Then turn over and secure to the mirror anywhere you wish.
Remember: The area you put the doily, will be the only spot in the mirror you will actually be able to see a reflection when we are done.
Place mirror down on flat surface. Shake frosted glass spray according to directions and then spray 7-12 inches away from the mirror in even, sweeping strokes.
Thin layers are the best way to go about this to avoid drips and other inaccuracies. Wait for each coat to dry (about 15-10 minutes) before applying the next coat. My mirror took four coats.
After the last layer is completely dry, gently remove the paper doily and double-sided tape from mirror. Clean with damp cloth and you are ready to hang.