Clear anything away from the area where you want to hang the mirror. This means that if you are hanging it above a mantle, you must remove any knickknacks.
Stretch a tape measure across the space where you are hanging the mirror; this will be where the top of the mirror goes. This line must be high enough to ensure that the bottom of the mirror will not rest on anything. Use a pencil to run a thin line along the tape measure.
Use the tape measure to check the distance from the top of the mirror and the hanging wire on the back. Then, use a stud finder to find a stud near the center point. Over the stud, run the tape measure straight down from the line you drew on the wall, and mark it at the same distance you got from the mirror.
Use a hammer to nail the hanging hook at the point you marked in Step 3. With the help of a second person, lift the mirror, and drop the wire over the hook. Use a bubble level to check that it is level.