Half baths are often used to accommodate houseguests, but they're also a convenient and heavily trafficked space for anyone in the home. For this reason, creating a half bath design that's stylish, welcoming and efficient is of paramount importance.
Since half baths are often located in hallways or other "standalone" spaces in the home, their design can often be freer, with more opportunities to add personality and eclectic style. Bold pops of color, contrasting textures and patterns for wallpaper and tiles, and fixtures and furniture that express their own distinct style are common features.
Aside from using a half bath as a design lab, one thing to consider is space. This is true of all bathrooms, but half baths in particular need an efficient design, since they're traditionally the smallest bathrooms in the house. Think about adding wall storage in the form of cabinets or shelves. A sink cabinet is probably a good idea as well, as opposed to a floating or pedestal sink.
Finally, when you're considering light fixtures for a half bath, think small and elegant as opposed to big and bold. The danger with larger fixtures is that they may overwhelm the rest of the design, so it's generally best to use a light touch when it comes to half bath lighting.