Spray cans are only appropriate when you are repainting at small scale. Repaint at big level will require a professional finish and therefore acceptable arsenal of car repaint equipment which includes filtered booth to avoid emission carcinogens and other environment damaging gases into the atmosphere and a high quality spray gun with different sizes of nozzle depending on the paint and finish required.
Before starting the car repaint jobs please make sure that the area is completely dust free. Performing car repaint is encouraged in a warm environment as it really makes your job easier and really enhances the finish of your paint. If you happen to be in a cold territory then make sure you have an access to a low bake oven.