Rooms that look expensive, because they were measured.

At least as wide as the sofa, ideally 6 to 12 in wider on each side.

It connects the furniture instead of floating between it. If you can walk between your sofa and your rug without touching the rug, it is too small.

Coffee table about two thirds the length of the sofa, sitting 14 to 18 in away from it.

Proportion, and you can still sit at the ends. Close enough to reach a glass without standing up, far enough to walk past without a bruise on the shin.

From the floor to the center of the piece, 57 to 60 in, even under a tall ceiling: go bigger or wider, not higher.

A starting point between standing and seated eye level, not a museum rule, and lower where you sit. It is lower than you think, which is why most art in most apartments hangs about a hand too high.

Rod as close to the ceiling as the bracket allows, never less than 4 to 6 in above the frame. Brackets 4 to 10 in past the frame on each side.

The window reads taller and wider than it is. No-drill brackets do this, so it survives a lease.

Sixty percent dominant, thirty percent secondary, ten percent accent.

It works in most palettes and most rooms. The pillows are the part you are allowed to change on a Saturday afternoon, and all they do is echo the ten.

Three layers in a room: ambient, task and accent, from at least three separate sources.

One ceiling light flattens everything under it, including you. Plug-in sconces and floor lamps add the other two without touching the wiring, which matters when the fixture is not yours.