Get the basics right, and prioritise them. Dont guess stuff, be ok with saying you don’t know or cant confirm and will get back with a confirmed response.
Assume theres a system, policy or procedure for pretty much everything until confirmed otherwise. Easier that way then finding you haven’t been going through correct approval processes for months because you didn’t know the existed.
Know your delegation of authority eg. Can you approve leave, budget, expenses, bonuses, pay rises, sickness etc.
Find out who your HR contact is in the first couple of days. Set up regular check ins with them. That will help you stay right on the basics. Keep a list of questions running for them in between those check ins. Ask them to do you an intro session on relevant processes and systems.
set up regular 1:1s with your team. Ensure each person has clear objectives, they know what they are and you know what they are. Get some kind of handover on any relevant matters for each team member (performance issues, promised development, pay reviews etc).
All the other stuff is style and personality customising. That’s all important, but cant make up for not getting the core line management stuff right. Without that foundation everything else flounders.