I had to drill ten holes through porcelain tiles to fix the brackets for a shower enclosure and another six to attach the shower mixer. I used masking tap to locate the holes and stop wander, started the holes using a set of them Screwfix ones pops mentions above to cut the glaze and then finished of with Erbauer Diamond Tile Drill Bit 8 x 80mm one these. I treated them all as consumables because I don't think they would have done many more holes and the best way to crack tiles is with knackered drills.
Erbauer diamond bits were recommended to me by my plumber mate and having 3 bathrooms/toilets to do over time I invested in the clamp as well. I thought it was good. Took all the worry out of skidding etc. for 15 quid it was worth it for me at least. https://www.screwfix.com/p/erbauer-diamond-tile-drill-guide/84524