Have a little something in each corner of the frame.  Even a little blank area can be something.  Avoid the boring corner with a listless expanse, empty of thought.  Do this no matter what other major design elements the photo may have.  The things in the corner will not be the subjects of the photo but will complete the frame.
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Find things to put in the corners
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Boy Scout Troop 174, Yorktown, NY.  Scouting Photography Pages at  http://troop174.info