A questions for car photographers?

I am entirely new to taking pro photographs of cars, and as it stands, my photos of a car look like crap. When you take out your d-slr, whatever make or model it might be, how do you go about doing an auto photo-shoot? More importantly though is how do you come to a conclusion that a certain photo which you shot stood out among others? Are there specific factors you take into account, such as light angle, glare, precise exposure, focal point (do you more often end up considering a car photo a success if it is an entire car in the frame or just the front headlight zoom, or strictly the side with a shadow) People told me that an unusual angle shot makes a picture more pro-like and I think its something different, but just because you put a tilt of 40 degrees doesn't make it pro. Is your decision of which picture is best perhaps comes down to just looking at the hundreds of pictures you shot and coming upon one you seem to like, or do you initially know, before even shooting that this precise angle and this light, with this much glare will be a very likely success?