Tip, if you need one. Put masking tape around tap area (on bath) first. It helps prevent slipping and if you do, hopefully masking tape will protect the bath.
I don't bother with masking tape but I do the following:
I carefully drill a 2mm pilot hole.
Then I check my measurements again.
Then enlarge it to 3mm, then 4mm then 6mm.
Secondly, I use a sharp hole saw (with 6mm pilot drill bit) and drill slowly, just scoring a neat circle to begin with then start using pressure when it looks right.
Process takes a good 2-3 minutes per hole but better than rushing and making a good mess.