The wall sconce won't be one of the main light sources for a room, it is more a complement. Make sure you install a dimmer for this light feature as it can set different moods for a room or hallway.
When installing wall sconces use this general rule; if your ceiling height is 8' to 10' the bottom of the sconce should be approximately 60" from the floor. The top should be eye level but make certain you are not looking directly at the bulb. Add approx. 12" for every foot higher your ceiling height may be. Now you know that rules are meant to be broken - this includes this rule. Because when hanging sconces as bedside lighting - the height should be at the same height a bedside lamp would be. Also when hanging sconces to specifically light a piece of art this rule will not apply either.
A personal pet peeve: don't hang the sconce so that when looking at it you can see up under the shade - it is hung too high.
Wall sconces don't have to hung in pairs. A single very decorative wall sconce can stand alone quite well.
Love the play on pairs in this room setting. Pairs of chairs, pairs of ottomans, and pairs of sconces.
Bathrooms are the perfect setting for wall sconces.
This swing arm lamp replaces a floor lamp.
Image Sources: Pottery Barn, Veranda, Global Views, Elle Decor, Decor Pad, Restoration Hardware, Architectural Digest