Keep Proportion in Mind
The general rule of thumb for hanging a mirror above a fireplace is to pick one that is at least two thirds the length of your mantel.
Consider the Shape
When choosing a mirror, consider the architectural features of the fireplace itself as well as the style of the room and the various shapes that it encapsulates. Is the mantel heavily ornate or is it more streamlined and linear?
Get the Height Right
Just like choosing the correct size of the mirror, getting the height right is key. It determines the overall appearance of the fireplace and affects the reflection you'll see in the mirror.
Secure the Mirror
A mirror can be pretty heavy, so to avoid any potential accidents and damage, make sure you secure it in place with appropriate mounting hardware.
Go for a Layered Look
Create a layered aesthetic by leaning a piece of art against the hanging mirror. Position it off center and continue layering other items, such as additional artwork or seasonal decorative accents, in front and around it.
Lean the Mirror
For a relaxed appearance and easier alternative, lean the mirror on the mantel instead of hanging it. It's less formal and gives you more flexibility when it comes to switching out your mantel decor since you're not putting any permanent holes in the wall.
Choose an Interesting Frame
While a mirror itself doesn't add color or a distinct image over a mantel in the same way that a piece of art does, an interesting frame can have the same effect.
Check the Reflection
Since a mirror over a mantel occupies a prominent spot within a room, check its reflection before hanging it in place. A mirror can be used as a design tool to bounce light around and visually enlarge a space, and since it may be one of the first things you see when you walk in the room, you don't want it to reflect a dark corner or cluttered bookshelf.
Use Multiple Mirrors
Hang a collection of mirrors for an interesting visual display that extends the range of reflection. It breaks up the reflection while maintaining an open and airy feel and gives the mirror an artwork-like quality.
Don't Ignore the Wall
Don't ignore the wall above the mantel, as it's a great opportunity to create a beautiful backdrop for your hanging mirror.