Two of the problems you may encounter when trying to drill holes in ceramic tiles are getting the hole started and using large bits to cut.
Often the masonry bits for ceramic tiles will wander around the smooth surface before they start to penetrate, making your hole in the wrong place. Start with a fairly small drill bit, an eighth to 3/16th of an inch in diameter. Turn your drill on in reverse, turning the "wrong" way. Now start your hole. You will find that it will not drill much, but it does not wander around. What it does do, as you can see in the photo, is make a little dent in the surface, almost like a centre punch hole in metal, that will allow your drill to get started.
Now drill all the way through with the small bit. These always drill easier and faster than larger bits. Then use this small hole as the guide hole for the larger bit, as you can see in the second photo. The larger bit will stay centred and not wander because it will follow the first hole. This technique will quickly and easily get a clean hole drilled in the right place without any scratches on the surface.