What should you treat first in a small home recording room?

It is easy to spend money on foam without identifying the actual problem. In a small room, the first priorities are usually listening position, speaker placement, early reflections and low-frequency behaviour. Thin foam may reduce flutter echo, but it does very little for bass build-up.

I would start by moving the desk and monitors, keeping the setup symmetrical, avoiding the exact centre of the room, and measuring or at least listening from several positions. After that, broadband absorption at first-reflection points and substantial corner treatment usually produce more useful improvements than covering every wall.

For people who have improved a modest bedroom or box room, which change produced the clearest audible benefit?