If the bridge wasn't the center of interest, your "negative" space doesn't cut the mustard - valueless.

A cropped version would have deleted much of the negative space.

From an exhibitor's point of view, cropping off the distracting sky area & left side would have enhanced the center
of interest.

Re: 2 & 3 - Cropping would have reduced negative space improving the composition.

Yet another poor example of "thirds" plus a lack of subject interest - even when properly cropped & you now also
claim to teach photography - unbelieveable!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Although your 2nd pic reduces the large rocky base, so of it is still needed that provides better emphasis to the falls

Since my pic examples didn't get thru for some reason, here they are again. As for your first pic winning a contest, it would have been interesting to see what the other entries looked like & Tracy's pic would have been better in a square format.

I must side with micolh, because there are many other things that must be considered & taken into account prior to shutter release when looking in the cameras viewfinder at your subject. The best place to obtain continual evaluations of your efforts is thru affiliation with a camera club or PSA, a national/international organization that
offers training in the photo arts. Re:1 - Though creative, it's too tightly cropped all 4 sides. #2 - The arm & white colored blouse are major distractions to the model's facial features. #3 - The large shoulder area overpowers the man's head, but cropping improves picture interest & also reduces distracting background. #4 - Another good model shot that needs to be cropped to better emphasize her facial features by deleting a distracting background.
#5 - More of the man's head is required, with a little dropping, would have produced a memorable image.
Now as for Tracy's "rules" pic - there's just too much negative space.

Re: pic #3 - too much negative space. Here's the crop for best subject interest.

Of the three pics, #2 is preferred - but in a tighter crop to enhance wave action.

Here is the list of stereo cameras & equipment that I have available for best offers + shipping costs.

The best presentation of the center of interest would have been a vertical format of the subject. Depending on your
location in MN, you should consider camera club membership.

Nice bird pic, but since it seems a little centered, suggest a tighter crop.

(Download)

Here's a suggested pic crop.

Good pic interest, but suggest a tighter crop to reduce negative space - darken bright distracting rock area &
replace the blah sky with appropriate cloud mass.