How do you manage people for the first time?
By accepting that it is a different job, not a promotion within the old one — which is the single adjustment new managers most often fail to make, and the reason so many are unhappy in the first year.
What actually changes:
Your output is now other people's output. Doing the work yourself feels productive and is usually the wrong choice. The uncomfortable truth is that a good manager's individual contribution should fall.
Your words carry more weight than you intend. A casual suggestion is heard as an instruction, and idle speculation about reorganisation becomes a rumour. This asymmetry catches everyone out.
You are accountable for outcomes you do not directly control.
Information flows differently. People tell you less, and filter what they do tell you. You must go looking for problems.
What to do in the first weeks:
Ask, do not announce. Meet everyone individually, ask what is working, what is frustrating, what they want to be doing in a year, and how they prefer to be managed.
Change little at first, unless something is on fire. Understand why things are as they are before reforming them.
Be explicit about how you will operate — how often you will meet, how you like to be updated, what you want escalated. Ambiguity makes people anxious.
Find out what your own manager expects, in specifics.
The mistakes that recur:
Staying the best individual contributor, competing with your own team.
Avoiding difficult conversations, which is the defining failure. Problems raised early are small; the same problem at an annual review is a crisis, and the person will reasonably ask why nobody told them.
Trying to remain everyone's friend, particularly when promoted from within a team — which requires an explicit, slightly awkward conversation rather than pretending nothing changed.
Micromanaging out of anxiety.
Passing pressure downward unfiltered rather than absorbing and translating it.
What actually helps: a mentor who manages, a peer group at your level, training that is usually available and rarely taken, and asking your team directly what you could do differently.