Depends on what type of tiles you have.
If they are standard ceramic tiles, with a hard glaze but a soft, almost plaster-like body, then the process is much as described in the previous posts. Apply masking tape to prevent the drill point skidding, use one of the ’shield’ shaped glass-drilling bits at slow speed, rotary only and light pressure to drill through the glaze and the tile body. I’ve normally used a size up on the hole I need in the wall - so if I’m using a 6mm diameter plug, I’d use either a 7mm or 8mm glass bit in the tile. Then use the correct size masonry bit to drill into the wall. The objective is to avoid lateral pressure on the sides of the hole in the tile. Simple process, just needs a bit of care.
If, as we do, you have hard porcelain tiles, that process really doesn’t work. You’ll wear out glass bits like nobody’s business, and use whole years’ worth of short words! For these tiles, you need one of the Erbauer self-lubricating diamond bits referenced earlier - there are other similar drills from other manufacturers. Still use masking tape, but start the hole by holding the drill at an angle to the surface then bring it square to the surface once you’ve started the hole. Modest speed, and a fair amount of pressure. Same consideration about the hole size in the tile.