I used an F-stop of 3.5 and a shutter speed of about 1/20 to isolate the strands of web from the rest of the background. The only thing I enhanced was to decrease contrast to make the lighting on the two sides of the tree less harsh.
The rule of thirds balances the photo by making the flower a more natural focus than it would be if it were in the middle of the photo. The foreground is much clearer than the background so attention is drawn to the front, the flower.
The rule of "Fill the frame" controls where the attention of the viewer lies. The background is not as obvious and so does not distract the viewer from where they should be looking. The roses are large enough that they block out most of the background, and the background is a little fuzzy to show that the focus should be on the roses.
In this photo, I used the rules of shadow and leading lines. The line of lockers leads your attention to the middle, and the figure in the middle is backlit by the light from the end of the hallway. The rule of light and shadow also highlights the figure in the center.