Fix the door before anything else
An inward-opening door eats the most useful floor area in the room. Rehanging it to open outwards, or fitting a sliding or pocket door, is often the single change that makes a small bathroom workable.
Check the landing side first - an outward door that blocks a stair head is not an improvement.
Choose fixtures by footprint, not by style
Short projection WCs, 500-550mm basins and 1500mm baths all exist and all work. A wall-hung WC and basin with concealed cistern free up visible floor, which makes the room feel considerably larger and makes cleaning easier.
The trade-off with wall-hung is the frame depth, which takes some wall space back. In a narrow room, measure before committing.
Shower over bath, or lose the bath?
If it is the only bathroom in a family home, keep a bath with a good over-bath shower and a fixed screen. If it is a second bathroom or an adult household, removing the bath for a proper shower enclosure usually produces a much better room.
A 1500mm bath with a decent thermostatic shower over is a far better outcome than a cramped 700mm shower squeezed in beside a basin.
Visual moves that genuinely help
Continuing the same floor tile under a wall-hung unit, using large-format tile to cut grout lines, running tile full height in the wet area, and a large mirror opposite the light source all make a measurable difference.
What does not help: tiny mosaic everywhere, heavy contrast borders at mid-height, and dark grout on a small floor.