What you'll need:
Step 1: Measure and cut out your fabric to cover the switch plate. Leave about 1/2", or a little more, hanging off the sides.
Step 2: Spread a layer of Mod Podge on the front of your plate, then place and center your piece of fabric over the glue.
Step 3: Turn the plate over an spread some glue around the edges of the plate. Fold over the excess fabric. You may need to add some more glue to make sure it sticks. Make sure your corners are nicely tucked! Wait 10-15 minutes for the glue to dry a bit.
Step 4: Flip the plate back over. Cut a slit in the fabric where your light switch is supposed to poke through. I just cut a slit from top to bottom of the rectangle, then made small snips up to each of the corners.
Step 5: Flip the plate over to the back. Place some glue around the hole you just made and fold the little bit of fabric back, just like you did the edges of the plate in Step 3.
Step 6: Flip it back over to the front! (Are you tired of flipping yet?). Paint a layer of Mod Podge over your fabric. Let dry for 15-20 minutes.
Step 7: Guess what? Flip your plate back over and paint a layer of Mod Podge over the bit of fabric that you'd folded over the edges. Let dry.
Step 8: Forget to poke holes in the fabric for your screws. Or not. Please don't forget to poke holes in your fabric for your light switch screws! I just poked a hole in the fabric after it was dry (with some sharp scissors!), and it worked fine.
And now, you're done! It really is super easy and barely takes any time (besides the drying part!).