White/Light Color Selection
Apply similiar color of appliances, cabinetry, and wall. White or light color will give a larger and bigger looks as if there's no boundary. White walls are great but maintaining them is a task then you have to clean them frequently. Here is small bathroom design by DVRasmussen.
Apply A Corner Sink
A small corner sink won't disrupt traffic lane in a bathroom and doesn't leave a wasted space. Put a cabinet unerneath vanity for maximum function.
Glass Partition As Shower Door
Instead of shower curtain, a glass partition that visually incorporates the tub or shower area make a tiny bathroom looks so much larger.
Right Placement
If you only have very limited space, skip the shower door and replace it with glass partition. It's enough to keep water splash. Avoid unnecessary space between bathtub, sink, and toilet.
Mounted Wall Towel Hanger
Instead of a big cabinet, consider install mounter wall towel hanger and shelf. It's simple and doesn't need large space.