Separate the owner from the possessed item
English-speaking learners often try to make the possessive agree with the owner. Spanish short possessives agree with the thing possessed: nuestro coche, nuestra casa, nuestros coches, nuestras casas.
Put the owner on one side of the screen and the object on the other. Ask two questions every time: who owns it, and what is the thing? The first question selects the possessive family; the second controls number and, with nuestro/vuestro, gender.
Teach su as an ambiguity problem
Su can refer to several possible owners. That is not a mistake in the language; it is a communication problem speakers solve with context or clarification.
Give students deliberately ambiguous examples and ask them to repair them with de + person when needed: su coche can become el coche de Ana. This turns ambiguity into a useful speaking decision.
Use objects that actually belong to someone
Photos of a room, suitcase, desk or shared apartment work well because ownership can change. Assign objects to several people and ask students to describe them. Then move one object to a new owner and require an immediate reformulation.
For online lessons, a simple drag-and-drop or pointing task can create enough variation to repeat the same forms without turning the activity into a list of disconnected sentences.
Finish by removing the visual labels
The final task should make students retrieve the possessive without a color key or table. Ask them to describe a shared house, plan what each traveler brings, or solve a lost-and-found problem.
If a learner says su and the owner is unclear, do not immediately correct the grammar. Ask ¿de quién? and make the student repair the message. That is exactly the communicative problem the form can create.