Figure Out Sizing
The very first step is to measure how much space you have to work with. If you’re hanging two mirrors over a double vanity, I would go a mirror that is at least 28”x23”, and for one large mirror over a sink, try for at least 28”x35”.
Shape
For a classic look that won’t go out of fashion anytime soon, go for a rectangle, circle or arch. If you’re looking to make your mirror more of a statement, try a more unusual shape such as a starburst or organic shape.
Style
Generally I recommend keeping a mirror in the same style as your bathroom. If you’re not sure how to define your style, try searching for images on Pinterest that will give you keywords such as minimalist, transitional or farmhouse. You can then search for mirrors in that style and customize yours to fit into your bathroom.
Frame
I usually choose simple black or white wood or metal framed mirrors for a clean minimalist look. Natural wood frames are perfect for a more farmhouse or traditional look. For bonus points, match the frame to the faucets and/or decor.
Bevel
With modern customization, you can now even customize the glass of your mirror. For a more modern or minimalist look, I recommend no bevel, but for a traditional or more glamorous space, add a bevel to create even more visual interest.