it is intentionally left vague, for the main reason, there is nothing that will work 100% of the time or a one size fits all. What you need to take away is more of make sure you understand your market/product/customers so you know what they want. Through experimentation ( building a product or feature based off of your expertise along with metrics of what your customers demand), you'll need to test, understand, and iterate, to determine what to do next. I don't even know if Eric Ries is/was a successful entrepreneur but he is considered a thought leader in practices made popular by himself and Steve Blank