My approach differs by client.
Here's one example:
Assess the way the individual thinks, the way they make decisions, what they think is important, what motivates them, and how they communicate
Start with a series of key interviews to undertand the surrounding dynamics
Add a qualitative interpretation of the results, including recommendations on how to lead, manage, and communicate with employees through transition.
Work closely with assessed client to develop specific behaviors and goals to close gaps in their performance.
Debrief key client, and with respect to confidentiality, recap for the client's boss.
Begin a coaching or mentoring relationship. Keeps the client on track with goals, client reports to their management on how well they're doing. Tangible, accountable, and effective. Weekly check-ins.