The moment success metrics are not clearly defined, the immediate action is to get them defined so everyone knows what they are aiming for. This is how I do it:
Ask the right questions of stakeholders – How do we measure success? What are we really trying to change? How do we monitor our progress?
Set Definite Objectives – Suggest clear, quantifiable project objectives if not previously done.
Align with the Team – Make sure that everyone is clear and in agreement on success criteria to prevent misunderstanding.
Document Goals – Capture goals, schedules, and assumptions for convenient availability.
Check-in occasionally to make sure everyone is on the same page and headed in the right direction. Without the initial criteria for success, time is lost and frustration ensues. You must define them up front and everyone must come to an agreement.