I'm no expert on primary, but went back after 15 years away into secondary, recently newbie, as a Cover Supervisor (in-house supply. Didn't have 'em when I was teaching 15/20 years ago!)
How long have you been out for?
Advice:
YY to having your own white board pen and maybe board rubber too. Teachers hide em.
Get your name and the l.o./work written onto the board asap, so that the class have something to focus on apart from you.
Ask for seating plans when possible. It changes the tone of a lesson completely if you can use the prearranged seating plan.
yy to asking about SEN/health issues . You should have notes on a lesson plan, but if not, the more folks who ask the better.
Read the school discipline policy - particularly on eg what to do if a mobile phone appears but have clear sensible expectations of behaviour of your own too. If told that "Sir always allows us to do X" you can simply reply that "I am not Sir so it doesn't happen today".
Have a simple starter activity in your bag that can be used in any lesson - eg sheets of plain A5. Ask the class to write down their names on the paper, and then:
1 thing they remember learning from the last time they did that lesson
1 thing they find hard to do
1 thing they are good at
It's a short achievable task, gives them something to do as soon as they come in the room, gives you an idea of their names, if you can read their handwriting, and of their ability.
I always carry blank grids for kids to make their own wordsearch up too, using key words from the lesson, if they have finished everything early. They can write definitions of the keywords at the bottom of the grid.
Best of luck