What To Do When You Inherit A Team
The first ninety days set the terms. Most new managers spend them demonstrating rather than learning.

Taking over an existing team is harder than building one, because the team already has a history, established relationships, and a view about your predecessor that you will not be told for some months.
Listen before deciding
The instinct on arrival is to demonstrate value through change. It is nearly always wrong. Practices that look inexplicable usually have reasons, and the reasons are frequently good ones nobody has written down.
Spend the first weeks in individual conversations with everyone. Ask what works, what is frustrating, what they would change if they could, and what they are worried about with a new manager. Take notes and return to them.
Ask what happened before you
Find out why the role was vacant. A predecessor who was promoted leaves a different team from one who was removed, and a team that has had three managers in two years will reasonably assume you are temporary.
You cannot address that assumption with a speech. You address it by being consistent for longer than they expect.
Find the informal structure
Every team has people whose influence exceeds their title — the person others check with, the one who knows why the system works that way. Identify them early and engage them honestly rather than routing around them.
Make one visible improvement quickly
Alongside listening, fix one thing the team has complained about and been unable to change — a pointless report, a blocked approval, a tool that does not work. It demonstrates that raising problems with you produces results, which is what determines whether you hear about the next one.
Be explicit about how you work
Tell them how you prefer to be updated, what you want to be consulted on, what you will decide and what you will delegate, and how you will handle mistakes. People spend enormous energy guessing at these. Answering them directly returns that energy to the work.
Then change things
After you understand it, change what needs changing — and explain the reasoning each time. A team that understands why generally cooperates. A team presented with reorganisation and no explanation defends itself.