Firstly, congratulations 🎊
I really enjoy being a HoD (most of the time haha).
Initially, observe and find your feet. Look carefully at what works well and what could be improved.
Then decide on what to prioritise first - remember, you can't do everything all at once. Better to do one or two things really well and get those embedded, than try to do many things superficially.
Spend time getting to know your team - as teachers but also as people - what ambitions do they have, what caring responsibilities do they have out of school etc. This will help you to support them.
Definitely agree with praising your team when something has gone well, they've worked hard through a tough week etc.
Stay organised- it's a hugely busy job - I'm a list person and I add deadline dates to it which are highlighted so I can quickly see what I need to do first.
There will be points where you feel swamped and overwhelmed- at these times, prioritise carefully - what absolutely has to be done, what can be delegated, what can wait?
Try to find a friend in another HoD in school- it helps to have someone in the same boat to vent with and ask advice of/bounce ideas off.
Most of all - remember to keep enjoying the classroom teaching. I love being with the kids in the classroom and even on the hardest days, it is still my favourite part of the job.
Good luck!