A short time back a member needed help drilling ceramic tile. There was many good suggestions. I find using a flat washer a little larger then the drill bit I'll be using. Mark the spot(X) then tape the washer over the X centering in in the washer hole with Duck Tape. Set the drill bit in the center of the hole and using a masonry bit I slowly drill until I penetrate the hard ceramic finish. Then take care to not drill to deep or out of round. A smooth hole will give the anchor better holding power. The washer will keep the drill bit from skating or wandering off center on you.

"OLDMAN"

How thick should the washer be to allow for the tapper of the bit?

Zipper:

Masonry bits aren't usually tapered. In fact they are quite blunt.If it is a problem then simply double up the washers. A smaller bit can be use to break the hard surface of the ceramic and then a larger bit to drill the finish size hole. Some situations all you will need is the tape to keep the bit from taking a walk on you. Again..use slooooooooooooooow  speed to start the drill bit.

"OLDMAN"

Now that we're back on this subject I'll put my 25 cents worth in.

The best way to drill through the ceramic finish on tile is to use a hole boring bit made for glass.  This is shaped like an arrow head, comes in various sizes from about 1/16, and will go right through the tile.  Another way is to use a small stone grinding bit to remove the finish first and then use a masonry bit to go the rest of the way.  Once you are through the tile you can enlarge the hole if you want using a smaller stone bit and just grind away until you get what you want.

Harry, Los Angeles, CA

I have found that a center punch will chip the glazing just enough to let a glass or masonry bit get started