Rule of thumb re: Rule of Thirds....according to Wikipedia, "the image should be imagined as divided into nine equal parts by two equally spaced horizontal lines and two equally spaced vertical lines and that the important compositional elements should be placed along these lines or their intersections!  This creates more tension, energy, and interest in the composition than simply centering the subject." 

That's powerful information. 

I photographed a swimmer from above.  By placing her in the bottom left corner of the photograph, I was able to show how powerfully she moved through the water.  It also begs the viewer to wonder where she came from and where she is going.

Find a powerful subject matter and use the Rule of Thirds to convey that power.