What size? I love how they make a room feel bigger.
Framed or unframed? Use as groupings, add light to a room...
check out these ideas: https://www.hometalk.com/search/posts?filter=mirrors
My mom always interspersed them throughout her house. If a narrow section between bedroom doors needed something, she used long narrow ones above each other. She also liked to work a few in her picture groupings.
Those are all great answers above. My thoughts were, put one or two where they would be useful, at the commonly used entrances, inside or outside the closet where you and guests take off coats and hats - knit hats are wonderfully warm/an absolute necessity and they wreak havoc on a 'do.
Then have you ever heard of feng shui? It's the Oriental philosophy of balancing a room (your house, and your life, if you want to get into it). For instance if you have an L-shaped room, position a mirror to reflect the cut-out piece to make the room a psychological square and feel more complete. There are whole books that explain the flow of energy and nature. I'm just a curious/voracious reader, but I'm turning my bed to face east and greet the morning sun to make my mornings go smoother the next time I rearrange my bedroom. Can't hurt; might help me personally. 😁