Prototype Testing: How Might We Learn as Much as Possible From the Participants While Also Giving Them Necessary Directions to Click Through the Prototype?

In recent iterative testing projects, I have been conducting concept testing with participants to learn about their experience of our mid-fi clickable prototype. In the prototype, there are 20+ screens, and they are of a linear step-by-step fashion. The selection of each step should feed into the following steps — and ultimately the final step.