If you're serious about learing the ins and outs of ps. Take a class. That being said there is much to be learned by not using it. A few shots from the philly auto show.
Jadito, hope you don't mind:
I took your last photo and made some changes. before:
After:
It was too cluttered with people and lightpoles coming out of the car, so I took them out. I also adjusted the saturation, hue and input/output levels. Now you'll notice that the background is pretty plain so in the future you might want to consider some clean backdrop like a building, water, etc..