Small rooms, tall doors
The most common brief I receive is some version of: we want it to feel spacious. The most common assumption inside that brief is that spaciousness is bought by the square meter. It is not. It is mostly bought by proportion, and proportion is nearly free.
A 14-square-meter bedroom with a 2.6-meter ceiling and a door of ordinary height feels like a hotel room. The same room with a taller door and a window that reaches the ceiling feels like architecture. The difference in cost is a few hundred units of any currency. The difference in daily experience is permanent.
The same logic runs through the whole house. A narrow hallway is fine if it delivers you into light. A small kitchen is fine if it borrows the view of a larger room. What rooms cannot survive is being mean in every dimension at once.
So when budgets tighten (and they always tighten), I protect proportions before I protect areas. Clients sometimes fight me on this in week six and thank me in year two. That trade is the job.