To apply paint evenly on a car's surface, it's important to use a spray gun and apply the paint in thin, even coats. Start by spraying the paint onto a test panel to ensure that the consistency is correct and adjust the gun accordingly. Then, begin spraying the car in long, sweeping motions, making sure to overlap each pass slightly. It's important to keep the gun at the same distance from the car's surface throughout the painting process, and to avoid spraying too much paint in one area. Allow each coat to dry before applying the next, and be sure to follow the manufacturer's instructions regarding drying times and application techniques.