My tips
Niche in shower/beside bath for toiletries (only possible if stud wall or build out)
Shower controls on the long wall, not under shower head, to avoid wet arm
Walk in shower with glass panel is best, means no rubber bits to get manky. However shower screen needs to be >1m to avoid splashing
Shower enclosures with sliding doors - you get what you pay for - more money = better mechanics and thicker glass
If water pressure is poor then avoid huge rainfall showerhead, choose smaller angled head for better shower
If doing shower over bath: install shower head on short wall above shower screen height. Put shower/bath controls and bath tap on long wall (or use bath filler). Then get a glass shower screen that folds a full 90 degrees so it can fold flat against the short wall, under the shower head. This way you can have an unobstructed bath.
Choose a basin with lots of ceramic surface area around the sink to put toothbrush etc. Don’t choose bowl style basins, collect dirt round where bowl meets surface.
Vanity unit with deep drawers is ideal for quickly putting things away of you like a clear surface.
Avoid black taps or dark tiles with hard water
Tiles with a bit of a speckle or pattern are much more forgiving in terms of showing dirt
Never use white grout
Large tiles in shower and on floor to reduce grout lines to go grubby
Matt stone resin (Lusso Stone et al) looks lovely but is harder to keep clean than ceramic
Brushed stainless show marks less than chrome
Don’t choose a loo with a “poo shelf”. Do consider rimless
Wall hung loos and sinks/vanitys are easier to clean under but cost more as you need the frame, concealed cistern etc
Get wediboard or marine ply and/or ditra matting laid under the flooring in any areas likely to get wet