In addition to what Brandon said, you could also turn off Always-on screen and Tilt to wake screen if you don't use these features. The first, obviously, means the watch will be blank when inactive. The second means you'll have to tap it to see the screen, it won't light up when you move your wrist to look at it.
These are in the Android Wear app; tap the gear at the top, then the name of your watch immediately under "Device settings". (This is for my Zenwatch 2, but I believe the app is the same.)