The main way to do so is to listen to the potential customer and not even mention your idea or that you are working on something. You must first understand their true problems, not your idea of what their problems might be, which many technical people especially do and rush into building a product that people may not even want. Ask them about their problems in their daily life and if you keep hearing the same thing over and over and it aligns with your idea, then build the product. Even if it doesn't, a repeatedly mentioned problem is still one that could have a good solution.
[1] www.talkingtohumans.com