I think the first shot is the best, but the sun is almost a "bullseye", which is not as dynamic as having it be a bit more off-center. Still, a good exposure and a good presentation of the image.
The second shot is the one that could have definitely been improved by turning the camera to vertical--the right hand side is just dead, empty space; a tall camera orientation would have produced a cool exaggerated apparent perspective distortion,with lots of keystoning, and it would have made that Audi look cool! The stripes on the placement and the white space in the lower right quadrant lead the eye right out of the picture.
It might sound odd, but one way to get better at this type of scene is to walk around with the camera AT your eye, from side to side, and really pausing to look, think,and question what you are seeing. Really LOOK, and stop and ask yourself. Look around at the entire viewfinder image; the thing is, today's 1.5x d-slr bodies have SMALL viewfinders, and things look, well small. We tend to mentally "see" our favorite part of a scene, and we tend to look at the central portion of the finder image--but mentally detaching yourself and FORCING yourself to scan all four corners of the frame, and forcing yourself to evaluate the image is the way to improve composition on static scenes like this grain elevator shot.
The third shot is not very good; too much green, not enough detail. Again, subject centered, but too much surrounding greenery with little real value. You need a larger flower, either via a closeup lens attachment, or a physically larger flower, like a large rose. The 18-55 isn't exactly a macro lens. The forced looking/evaluating tip I gave you in the middle will help you evaluate photos like #3, and avoid even pressing the shutter until your eye tells you you have a good viewpoint and a good image.
Enjoy the "free film" a d-slr provides; in six months you'll be kickin' butt!