Small bathrooms are tough to design. On the one hand, because they are compact, you save money on materials because you are using less materials. On the other hand, small bathrooms are small, and no one likes being cramped.
Avoid having anything that sticks out from the walls especially in very narrow bathrooms.If you have a small space with a tall ceiling, play that up by painting the ceiling a light blue with some small clouds to draw attention up.
To give the illusion of more space eliminate as much visual clutter as possible when selecting fixtures and materials: Clear shower enclosures with minimal hardware; swinging doors rather than bypass if possible.