Here's my take on your pics.
First of all try using the Av setting which gives you a lot more control but still sets the shutter automatically.
Second, you can adjust which point the camera focuses on. I usually have mine set on the center point, press the shutter halfway to focus and lock in the exposure, recompose the image, then shoot. That way I always know where the focus is going to be. It's the top right button on the face of the camera, also used to zoom into an image when reviewing it.
Third, be mindful of not just the time but the weather. If it's clear and sunny, early morning when the sun is just above the horizon or evening when the sun is just about to set, is your best time to shoot as they produce long shadows and really beautiful light. Shooting when the sun is directly above creates dull shadows and a high contrast between the lights and the darks, like you have between antenna and your dark car. You generally want to have some detail in all area's of the picture, both the highlights, and shadows. Learn to use the histogram both on camera and in photoshop. While on the topic of photoshop, learn how to use Lightroom as it will greatly reduce the time you spend editing. You can make minor adjustments to many pictures at the same time. If you find yourself making major edits to the lighting, make a note of that and adjust that in camera next time.
Composition is very important as well. You don't want to have things coming out of your car, or anything too complicated being really close to the car, as the car is the main focus. If you parked your car about 20 feet further from the antenna, stepped away from the car and zoomed in to 55mm on your lens, you would have a much more appealing image. Be mindful of what interacts with the main focus of your image.
To start, read up the three basic elements of your camera, shutter speed, ISO, and focal length and how they influence your picture.
Experimenting on your own and looking at the results on the computer will help you understand the functions better. Posting up the pictures for a critique is good too but a more photography related forum may suit that better.
And lastly, one of L4P's own is a great source of both inspiration and idea's
notbland's deviantART gallery I specifically linked starting at the end of the gallery because if you start with the recent work it's a bit overwhelming. You can see how he goes from roughly your skills to having Top Gear and Dodge as clients.
