If I’m overwhelmed by a room and just need to get it tidy quick, I grab an empty box and put everything in it that doesn’t belong. If I’m on top of things (read: rare), items in that box will be put away over the course of the next few days. But alas there the current box sits.
I second Simplicity Parenting! Also, Outer Order, Inner Calm by Gretchen Rubin – getting to that inner calm is so, so motivating.