Hanging the Mirror
Position the mirror first on the wall or door. Hang it where is it easy to use and where taking a quick glance does not take you out of the way.
Hang a full-length mirror just above your wall's baseboard. Position it as low as you need to see your shoes. If possible, avoid placing the mirror's bottom edge flush to the floor to prevent any damage to the lower edge of the mirror's glass or frame.
If your mirror is not a full-length mirror, then hang it at a level where you can easily see your head and upper body.
Hanging the Shelf
The shelf above a full-length mirror should be positioned so that you can pass by the shelf without bumping your head but so it is also within arm's reach. This may mean placing the shelf a few inches above the mirror. For half-length mirrors, a shelf hung below the mirror may serve as a counter for accessories, necessities or mail. As long as the mirror is positioned to view the upper body, a shelf below it will feel like a mini counter.
If you are hanging a mirror and shelf above a piece of furniture, then position the mirror a few inches above the furniture to keep it from bumping the mirror. If you place a shelf above the mirror, you don't have to worry about head clearance as the furniture will prevent anyone from walking close to the shelf. The shelf does need to be within arm's reach, however, if it is being used for convenience and not merely decoration.