Organizing is what you do before you do something, so that when you do it, it is not all mixed up.

A. A. Milne (1882-1956) English poet and playwright [Alan Alexander Milne]

(Attributed)

Widely quoted and attributed to Milne, but I can find no instance of it with an actual, proven citation.

Ross Webber in Management: Basic Elements of Managing Organizations (1979) gives the following:

In A. A. Milne's childhood classic Winnie the Pooh, Christopher Robin tells his group of stuffed-animal friends that before they can search for the North Pole they ought to get organized. Pooh asks what getting organized means, and Christopher replies, "Organizing is what you do before you do something, so that when you do it, it is not all mixed up."

All well and good, and Christopher Robin does organize such an expedition ("expotition") to the North Pole in that book -- but never says anything of the sort. It is possible that the line derives from a Disney animated adaptation, but could not confirm this.