well if you keep the glass lubricated it'll be less susceptive to cracking, and if you wrap a few layers of masking/duct tape around the spot you wanna drill it helps keep the bit in one spot (so it doesn't jump around) and it also helps if the glass should break, to not go everywhere, also adds to the structual integrity of the bottle giving it bit higher tollerance level, after the holes are in it, just remove the tape... as far as lubrication i've always just heard of getting a water bottle or something where you can drip a few drops of water every few seconds, you dont' want water everywhere...