A triangular bathtub is a better choice than a square one
Triangular bathtubs are quite space-saving too. So, you may choose one such bathtub instead of a square one for your small bathroom.
A glass shower cubicle will also make the bathroom look bigger
Glass shower cubicles are also good choice for small bathrooms. The glass doors don’t break the space, but make it appear bigger than it is.
Add more light fixtures
Small spaces should be also well-lighted, in order to appear bigger. So, feel free to add more light fixtures in your small bathroom.