Measure for the cutout and place the mark on the face of the tile. Put two to three layers of masking tape on top of the mark, then re-mark the center mark on top of the tape if you cannot see it through the layers.
Don safety glasses. Clamp stand-alone tiles not already installed on a wall tightly down onto a cutting surface, such as a scrap piece of wood or a work bench. Drill straight into installed tiles without concern. Center the drill bit on top of the mark.
Squeeze the trigger of the drill slowly and allow the drill bit to gently dig into the surface of the tile. Once it has broken past the surface of the tile, pull the trigger down completely and apply slight pressure to the bit.
Push the drill bit into the tile until you punch through the back.