Instead of saying what you don’t want, explicitly say what you are asking for more of.
Even with neurotypical kids in a dance or cheer camp, saying “Remember to point your toes” makes for a much more positive experience than saying, “Don’t flex your feet.”
Also be direct in expectations.
“The kitchen is a mess,” is not the same as, “Please do the dishes.”
Also, ask for things in the time that it can be executed.
I need to to know that I should buy batteries when I am in the store (or at least when I can write it in my shopping list), not when driving the car somewhere else.