Terrazzo floors can be tricky to adhere to particularly because of the smooth, glossy surface and the potential of having wax buildup. The very best way to prepare the floor is to rent a concrete scarifier. This will roughen up the surface to give the thinset something to grab onto.

Here is an example of a scarifier: www.floor-equipment.com/...

Another option would be to apply a chemical stripper to remove any wax and then rough sand the floor to remove any sheen. If you choose this option use a standard grade, portland based thinset (non-polymer modified) and mix with a liquid latex additive instead of water or simply using an epoxy thinset. Also, when gluing the tiles down be sure to force the adhesive into the substrate using the flat side of the trowel first, and then use the notched side. Also, as with tiling over any concrete floor, cover any cracks with a crack isolation membrane following the manufacturer's instructions.