More than communications skills, lean techniques to discard useless features with no value, more than ask "what do you want?" or "is there anything else?" to the customer.
Reading the book Agile Project Management of James A. Crowder, it says: "Organizations must strive to provide an environment where budget is not centered on time and motion, but must be centered on the perceived values of the objectives of the project.... In classical EV change is bad and uncertainty is worse".
From the book Brilliant Agile Project Management of Rob Colle & Edward Scotcher: "Agile embraces change and even encourages it. Change is not seen as the enemy, it's seen as an important part of the evolution of any good idea."
In an agile approach everything is speculative and scope never is closed until customer is satisfied.
It looks like to me that these statements are for internal projects in software companies like Facebook, Uber, Airbnb, or even in in-house projects where there is an initiative to improve processes continously.
In a context that you handle projects with external customers and projects with ad-hoc development, we are limited by the triple constraint all the time. What are the techniques you use to set up scope and minimize the number of iterations if we are in time-restricted contract?
*Triple constraint is the name that PMI uses to describe restrictions on any project in Time + Cost + Scope (+ Quality in 6th version of the PMBOK) Any change on any of this restrictions will affect the other. A change in time, it will affect your cost, any change in scope affects time and cost and so on.
This is so restrictive, fixed and old in terms of agile. Once you have your baseline, you cannot change it, but through a formal change process. With external projects based on classic perspective, you manage contracts to deliver a product or service in a specific time and in a budget.
That's why in classic approach change is bad. If you change your baseline (time or cost or scope) it will drive you into a rework or reschedule. Nevertheless in agile, change is accepted all the time. Kind of 2 philosophies conflicting each other in change management, but we need to limit changes in a way to fulfill with deadlines.