Use the belt sander to completely scour the surface of the old tile. Mastic and thinset will not bond to a ceramic surface, so the only way to ensure a structurally sound installation is to scuff the old surface so that your adhesive will bond properly. Use the roughest grit sand belt available, preferably a silicon carbide sand belt as they are specifically made with hard surfaces in mind.
Vacuum the surface of the wall completely. You need to eliminate any particulates that could potentially harm the bond of the adhesive.
Using your notched trowel, apply a layer of adhesive on the wall where you want to install your new ceramic tile. Make sure there are no uneven sections, and avoid leaving any bare patches. Spread only a small area at first until you are comfortable with the tile stacking process, otherwise your adhesive could dry up and prevent an adequate bond from occurring.
Apply a piece of ceramic tile directly onto the adhesive. Using gentle pressure, move the tile slightly in all directions to ensure proper bond between the adhesive, the tile and the substrate.
Use tile spacers to space between the tiles. Repeat step four for every piece of tile placed on the wall.