Grouting is not too difficult to do. However, most people will use a finger to smooth the grout and then accept the fairly rough finish that results. However, I learned the professionals tip for producing ever so smooth grouting that makes your tiles look perfect. It really is worth following this advice to get the professional look to your bathroom.
The great news is that the extra tools cost about 30 pence and can be bought from any supermarket.
What
you are looking for is a kitchen sponge like this. The brand is immaterial
and it isn't the scourer on top we are interested in.
The yellow synthetic sponge has a fine cell structure making it perfect for smoothing tile grout.
The technique is to wet the sponge and run it over the grout in short, light and above all straight and parallel strokes.

Be careful that the sponge always stays parallel to the wall and after a few minutes of gentle smothing you will have perfectly finished grouting on your newly laid tiles.