Personally, I've had an experienced manager and took great inspiration from him.
A few things I fell into:
- it was a lot faster for me (I.e. experienced senior dev with context knowledge) to finish a task than for me to assign it to someone less experienced who has to learn the context and takes 5x as long to do it, with lots of help needed from me still. This yielded me not building up my team either in experience or knowledge.
- I assumed deadlines I got told were set in stone and my job was to meet them. This made business-y people happy. It made everyone else (including me) miserable. I had to learn to say no and push back, it very much changes between companies but most of the time I found it to be a negotiation and either the deadline could move or I had to argue to exclude things from the scope to make the deadline reasonable.
- on the above, everything takes at least 3-5x as long as I think it takes. If things finish early, great time to give my team some slack, add in additional QA work like extending tests or repay some tech debt. Delivering something early gives a pat on the back for us but no discernible benefit to the team.
- every time someone said "you'll have time to write tests/repay tech debt/upskill later once X is shipped" it never came true. Those things have to be built into delivery scopes, and it's a constant battle - if you don't do this, nobody else will.
I'm sure there were other things too, but these are the ones I mainly recall. Talk to your team, ask for feedback. Every team, project and company are different - you'll have to adapt.