Think of the one tile you want to include in your design. It could be a specific accent tile or it could be as general as knowing you want a specific tile type. Once you have your ideal tile design, use this as a starting point for the other tile you will choose in your bathroom design.
The typical formula for bathroom tiling is flooring tile, shower/tub surround, and an accent tile which is used as a focal point. Having more than these three tile choices can make the bathroom seem busy and can make the tiles clash.
With so many colors and patterns, tiling provides the perfect opportunity to take a risk and give your bathroom some personality. It is a good idea to limit your design to one show stopper as too many big design choices takes away from the wow factor.
When it comes to cleaning, porcelain and ceramic tile are the easiest to maintain. Tiles made from natural stone have to be sealed and tend to hold dirt more due to its many pores. If you are looking to use stone consider using it on the floor in a dryer area. Glass tile makes a great wall or accent tile. Try to keep it off the floor as it is very slippery.
Scale is also important to consider. Large scale tiles are in style right now but cause the floor to be more slippery. The bigger the tile the bigger the space seems.