At work, our bathrooms have a light and a fan. The switches are together on the wall, the one for the light is on the right, and the fan's is on the left. Additionally, the fan's switch is black, and the light's is white. So, the switch for the light is the one in white on the right.

People using the switch have three ways to index the memory: the position (right,left), the color (white,black), or the mnemonic(light-white-right). Additionally, the switch for the light is closest to the door, which is good for groping hands trying to find switches. Alltogether, it is surprisingly well-planned.