The discovery method I find most useful personally is observing. I consider myself a visual leaner and creative designer, given my graphic design background. With that said, whenever I begin the discovery process in creating a new idea or concept, I always seek to visualize a problem as physically demonstrated and draw it out.
What my drawing would include is dependent upon whatever my observation focuses on: the environment(s) where a problem takes place, the points of dissatisfaction the user(s) have in encountering an issue by an existing product or an element not yet countered by a new product, and some key background facts about the demographic who I aim to target (this is mainly shown in brief side notes next to my drawings). Now usually in this same document, I begin to draw some rough sketches of ideas that could solve one to many issues witnessed from my observations. The goal for me here is to address all issues in some way, which inevitably leads me to several sketches for potential prototypes until they’re eventually narrowed down.
Ultimately, the method of observing is very effective for me because the problem is being presented as a case study where reactions that are elicited forms the basis for thinking about solutions in a similar (visual) medium. Yes, other methods like brainstorming and research often happen at this point too (especially the former), but I’m specifically talking about taking what was seen and translating that into what could be seen on paper.
If multiple designers within a team do this separately and later compare and contrast their ideas visually, I strongly feel that a story is being told, where the intent is to find the “best” one, either by one designer or a collaboration of two or more. I just get the sense that openly discussing ideas without a visual following observation leads to forgotten notes, and not enough in-depth focus on the issues discussed. If we can get a perspective (within a person’s shoes facing a problem head-on), a stronger and more natural discovery process would most likely result in conceiving potential ideas.