WOW last two... ?
"Once you fully understand the rule of thirds and have taken hundreds of photos with it in mind and have made your eye look for it in every printed image - forget it."
I think I know what you are saying... That once you understand the rules you will know when and how to break them.... am I right? (they are guides really not real rules)
"A 'viewer' can help you to compose a scene.
A simple piece of opaque cardboard, say 4" x 6", with a rectangular cutout will serve. Make the ratio of the cutout identical to your film/sensor format. Then glue four thin wires in position to divide the cutout area into 9 equal rectangles [rule of thirds].
Total cost? Small. Usefulness? Large."
I am sure that this is effective. But in my experience peoples eyes / brain combo are quite good at trisecting (cutting into three) views. I would imagine that this is REALLY fiddly. Of course, I have not tried it, so I may be wrong.....
I would be interested to hear from anyone who has done this as to whether it was a useful training aid..