Collecting acorns to eat - how/when?
While I have never collected acorns to eat, only to feed to animals, I have foraged and served beechnuts and chestnuts, and the same principles apply.
Ripe acorns will fall - so picking them up from under the tree is perfectly fine, no need to climb and risk anything.
As for most nuts, fallen acorns are protected by the outer shell and can withstand being on the ground for a bit. As they need a cold phase to germinate, they will remain mostly unchanged during the autumn, giving you a generous window to go out and forage.
You want to pick large and plump acorns, leave small, cracked, soft or otherwise damaged ones to the wild animals. You should wash them when you bring them home1 or before processing them. This is also a good occasion to sort out the random hollow acorn, because they will float.
Then proceed as per your chosen recipe.
1 If you don’t process them immediately after foraging, make sure they are dry on the surface to prevent mold.