One of the first step is to ensure all core members of the team are given exposure to the Contracts (Scope, Assumptions, Dependencies etc.). I have seen so many times in projects one of the key reason of scope creep is because no-one except the Project Manager or Delivery Leaders have any insights into contracts.

Let me tell you how I tamed scope creep on our last major upgrade: First thing I do is maintain a visible "scope wall" – a shared document listing our core requirements and explicit "not-in-scope" items. Whenever someone suggests a new feature, I ask them to trade it for something of equal effort in our current scope. I also started doing weekly 15-minute scope check-ins where we review our progress versus initial goals. The real game-changer is to teach the team to say "Yes, in version 2" instead of just "No." That way, good ideas aren't lost, they're just properly scheduled. And always keep your MVP definition clear – I literally have it printed and stuck on my wall. It's saved me countless times from the "just one more feature" trap.

One thing I’ve found useful in establishing clear objectives is to clearly and completely define the desired outputs. Anything that’s not necessary to creating the outputs is optional or out of scope.

Talk to the customer and build a HoQ matrix, VoC, PughMatrix, etc., whatever makes most sense to the customer. Primary goal is to identify the most important aspects from the customer's viewpoint. Prioritize quality and customer satisfaction by having your best technical team members (2 to 3) work closely with the customer. This will help acheive two goas: 1. avoid wasting valuable time and resources on things that aren't all that important to the customer, but may be captured as must have's in the initial requirements 2. ensure that your team are hearing directly from the customer, and not using their own interpretation and implicit assumptions about the requirements.