The trick to not damaging the wall tiles is once the hole positions have been marked, cover each location with a cross made up of two pieces of masking tape – then if the drill slips across the tile surface the tape will help protect it from damage.
You might be lucky and be able to drill through the tiles with a standard masonry drill, but my advice is to start using a masonry drill then use drills specifically for the purpose, like these:-
http://www.screwfix.com/p/erbauer-tile-glass-drill-bit-set-3pcs/53634
While drilling, regularly cool the drill tip by dipping in a cup of water – it’s surprising how tough ceramic tile material is. By the time you have drilled 4 holes using the tile drill bit, it may be at the end of its service-life (especially if not kept cool during drilling).