Your first step is to find some molding that will compliment your home and the mirror. You can choose something really simple or build up some chunkier pieces for a really unique look.
For this medicine cabinet, I picked out two compliemtary moldings and built the frames so that they would fit around the outside of the cabinet and flat against the wall so I can still open and close the cabinets. I love the way that they turned out - and they're one of a kind!
This wall mirror is fine - it will serve its purpose, but the addition of a frame will make it a statement rather than a functional piece.
I stained this molding to match the wood in the walk in closet. Once the mirror is secure in the frame, use some "l" brackets or a backer board to secure the mirror to the frame. Be sure that the screws are not so long that they will go through the front of the frame.
For more information on how to build a frame, check out my website! I'm Mrs. Fixit and it's just that simple!