I had to replace two wall tiles in a wet room as the customer tried to put up a new shower rail but the tiles broke when he was drilling the holes.
Drilling holes in tiles
Step one; You are going to need the right size tile bit these are different to standard bits.
Step two; Mark the tile where the holes are going to be drilled then stick masking tape on these marks and remark on the tape (tape is to stop your bit slipping)
Step three; set you drill off hammer action & on to low speed, drill the holes.
Step four; ensure that the plug that you use in the holes go pass the tile because if the plug is touching the tile when you tighten up the screw it is quite likely to crack the tile.