Depends on what I am categorizing, but I place grocery items on the conveyor belt based on what type of food it is, and where it will all get packed up in the house, that way I don't have to rummage through piles of bags to look for everything that should belong together. Makes it more efficient to unpack the stuff later on.
When it comes to organizing my closet, I tend to put shoes I use for the summer up front, and the winter ones in the back. I put dress clothes in a spot where they are safe, and the stuff I use more often towards the front. Quick access!
Filing things, I tend to do it in alphabetical order, and base it on what type of files are in there.
When I'm organizing things, I like to have the stuff I access the most often to be up front.