I have a hard time evaluating prints from a scan. I never know how much of the damage is done by the photographer, their scanner, or my lousey monitor. But here goes....
#1: Compositionally this is done well. The horizon is low to emphasize the cloudy sky, and the silhouettes of the trees frame the sky. There isn't anything that competes for attention with the sky. Subject wise, every photographer and thier brother/sister are shooting cloudy skies silhouetted by trees; either you need more exciting trees, or a more exciting sky, or both.
#2: The white sky has got to go. Does the print have more color? Compositionally this is too cluttered. Get up closer to that redbud (or whatever the pink tree is) and fill the frame with the pink foliage and twisty branches. If you fill it up enough, I might even be willing to overlook the white sky.
#3: Is the red tree the subject? Move it out of the center and get a lot closer. Get rid up as much blank grass and white sky as you can. Changing your point of view so that the red tree has a background of dark green trees will really bring out the red. If the red tree isn't your subject? Well, once you've got something red in your picture it will always compete for the viewers' attention.
#4: Too much clutter, too much blank grass, too much white sky. The tree in the left center looks interesting. Get up close to the trees and the shadows. I want to see a frame filled from edge to edge with wood and shadow. Try composing your subjects so that your most important subject breaks three sides of the frame.
#5: Change your point of view so that you isolate the red and tall green tree against the blue sky. A polarizing filter will increase color saturation, and make the blue sky darker. Lose the building and any bright white clouds along the edges (unless you can get a point of view where there are clouds all across the sky). Bright white objects attract the viewers' attention away from the subject.
#6: This is the one I like the best out of these pics. A little closer might be good, and get rid of the buildings(I'm just finding them distracting). The lighting is too harsh. Come back here at sunrise or sunset and take this shot with nice glowing, warm light.
There's my critque; it can be summed up as get closer, fill the frame, avoid clutter, and as little bright white sky as you can get. Pay attention to what is at the edge of your viewfinder.
Do you think these are your best pics? Let's see some of the others that you like but people didn't choose.