I open all the bags and give the minifigures to my son to build and lose the guns, tools, helmets, ect. Then I dump the bags and organize by color. I start handing pieces to my daughter 1 or two direction numbers ahead of where she is. While she is building, I sort the pieces further by shape and size. I try to fit all the same type of pieces together so they don't get lost when my son is done building the minifigures. When I am several steps ahead of my daughter, and all the bricks are organized, I start helping my son find the lost pieces.
When building alone, I do pretty much the same thing, only I work bag by bag and have several glasses of scotch.