Make it small
A tray or basket creates a visible limit.
Give it one purpose
Incoming papers or returns are clearer than a general miscellaneous pile.
Review on a trigger
Empty the zone when it fills or at a regular time.
Keep critical items elsewhere
Important documents and valuables need deliberate storage.
Practical boundary. Measure first, respect product load limits, and do not improvise wall, ceiling or overhead installations when the structure or appropriate hardware is uncertain.