Tools/Supplies (Click here for links)
Trim (I used 1in lattice trim)
Tape measure
Saw (hand saw & miter box or chop saw)
Paint
Screws and washers
Mirror adhesive
Wood filler
Sand paper
Caulk

Basic Steps
Move mirror up (optional)
Replace clips at top with washers and screws to get it flat
Add scraps at top to glue trim to to cover washers
Cut trim to size
Paint both sides of trim
Glue trim to mirror
Wood fill gaps in corners
Touch up paint
Caulk visible sides (optional)

Detailed Steps

Optional – I moved my mirror up a few inches. When I did this in Fort Worth to a larger mirror I didn’t move it up so it’s whatever you like best! 

• I removed the top screws and the mirror was not glued to the wall so I just slid it out. 
• I moved the bottom mirror clips up and patched the wall where the old ones were, then put the mirror back. 

Replace the mirror clips at the top of the mirror with washers and a scrap of wood behind the washers to keep them flush so it’s as flat as possible 

Next you’re going to put scraps (that are the same thickness as the mirror) on the top of the mirror to attach the top piece of trim to 

You can’t just attach it to the mirror or the washer would stick out or the top.

Now measure the mirror. Be sure to account for the scraps at the top.

Mark your trim and cut it at a 45-degree angle using a miter box and hand saw or a miter saw 

I find it helpful to hold the trim up to the mirror and mark the angles I need to cut so I don’t get confused when cutting.

Lightly sand your trim then paint both sides

Put adhesive on the outside edge of the mirror. If you get too close to the inside, the glue will show in the reflection. 

I put the bottom on first, then the sides, then the top. 

*Optional* use a nail gun to attach the trim to the wood scraps on the top 

Caulk the visible edges.
Wood fill the corners.
Touch up the paint.

Total cost for me was about $20 since I just had to buy the trim and glue 

There are also companies that send you the frame and you just assemble it and stick it to your mirror via adhesive strips. Great option but definitely more expensive.