Painting a car well is what makes the whole artwork look like it was done by a pro. When I started drawing cars I focused to much on painting the cars right instead of looking at the proportions of my car painting. So before you start shade and paint be sure that you are satisfied with the cars lines so far, because once you start paint and shade it will be very hard to change any lines. So if you are absolutely sure, then lets start shading the car.
One big tip here is that you start at the upper left corner (or upper right corner if you are left-handed). This is because it reduces the risk of the car paintings to get all messy. So start from the upper corner! Think about how you want the whole painting to look, try to get a image of it and then you start slowly adding with your pencil this to the background. If you need reference photos then go a head and get those, these will help you not to mess up to much on the background proportions. Dont start with the darkest area, instead start coloring the lighter area of the background of you car paintings, and then go to the darker areas gradually. Then when the upper corner is done, then start moving the center area of the...