Before tackling any tiling project, it is crucial to begin with properly prepared surfaces. Failure to prepare a surface thoroughly can result in uneven tiles that protrude in odd places.
You’ll need a hammer, chisel, eye goggles, filler and coarse sandpaper.
Regardless of whether a wall or floor is being prepared, removal of the existing tiles is recommended. Use of a hammer and chisel provides the best way of doing this. Before starting, wear protective eye goggles and clothing and make sure the floor is protected from any debris that may fall.
Ensure you clean and dry all surfaces after removing all the tiles, and brush away all dust and debris.
If the surface is in poor condition, some plaster bolster may be needed to fill holes, and filler may be required for the repair of any cracks or other holes.
With all blemishes and cracks filled, smooth the surface using an electric sander or coarse grade sandpaper. The surface should be worked on until it is smooth, make sure you’re wearing a mask, and open windows to increase ventilation. Make sure you remove all the dust from both the substrate and the tile to be laid to ensure the tile adhesive bonds perfectly to both surfaces.
Source: http://www.homeserve.com/videos/build-renovate/how-to-prepare-for-tiling