Very small bathrooms can be a big challenge to decorate, because you don't want to make them feel even smaller. How you tile the bathroom is potentially the biggest factor in the feel of the room--and it's not something you can easily change if you get it wrong. Carefully consider tile size, style and colour when choosing your tiles. Lay out some test tiles on the floor in the bathroom ahead of time to get an idea of how it will make the room feel.
There are two schools of thought when it comes to tile size in a small bathroom: One, that small mosaic tiles work best because they allow the creation of intricate designs and patterns on your small floor and walls, and, two, that very large tiles work best because they give the illusion of a big, bold room. Whichever direction you go, go to an extreme; don't use a standard six- or 10-inch tile, which is too big to make any effective design in a small space, and too small to give the optical illusion of a large space.
What material of tile you choose for your bathroom is going to depend partly on your size scheme. If you're going with very large tiles, then ceramic isn't a good idea for the floors (large ceramic tiles are more susceptible to cracking). In that case, go with marble or another polished stone, which will be more expensive but can be laid in large sizes without much danger of cracking. If you're going with mosaic tiles, then ceramic is fine, though glass may look better. Whatever you use, make sure it's a high-density glazed version; flat matt tiles aren't good for bathrooms because they don't repel moisture or clean up like glazed finishes do.
In terms of colour, lighter is almost always better for small spaces. Dark colours tend to visually close in a room, while lighter colours open it up. Some variation of colour and design also helps to give the feeling of something going on visually, which makes the room feel less enclosed. You can purchase mosaic tiles in mesh-backed sheets that have multicoloured designs already arranged into the tiles, or you can cut the mesh in any configuration you want and mix it up with different colours.