The most effective way to learn users' needs is to give them a prototype and gather feedback from the experience. This goes perfectly with the Agile Methodology to always deliver after each sprint. Which allows for faster feedback and the product continuously moving toward the customer's desired product.
Reference:
H. Gomaa and D. Scott. 1981. "Prototyping as a Tool in the Specification of User Requirements". Fifth International Conference on Software Engineering. IEEE Computer Society Press., Washington, DC, USA.
