Masking tape on the tile. Mark the point to be drilled on the masking tape. Helps stop the drill bit slipping too.
Latest update, got all the bits and pieces out and ready to go and now see the wall plugs and screws are loads bigger than the 6mm arrow head bit I was sold yesterday (even though I took them with me and showed them) Been to another shop and their recommendation (which i bought) is an 8mm diamond tipped thing that looks more like a grind stone than a traditional drill bit. Additional advice is to use dry. This bit doesn't have a point so center punching or masking tape isn't going to help stop the wandering.
Also push your rawl plugs through the tiles completely or else you'll crack your tile when you tighten your screws.
Take it steady and drill into the grout if you can. Don’t push too hard or you might damage the tile, let the drill do the work.
Why not pay somebody to do it. Yes, this is a diy thread, but two trips to the shops, two drill bits, still asking on here?
Me, I'd use a 8mm bit to drill the tile then a 6mm masonry bit to drill the wall behind it. If the tile is ceramic use a masonry bit, porcelain use a tile bit. Edit, Asterix's advice above is good. If you **** it up it'll cost you even more.
I once drilled into a live wire whilst putting a shelf up. It threw me off the ladder. Now DIY advice...
Did you put the tiles up yourself? If they have just been dabbed rather than spread you could be in for a cracking time. I’m stripping paint at the moment rather than watching paint dry at KCOM