Use a flexible sanding block and fold the sandpaper around it. The block will apply even pressure to your car's various bends and creases. Keep the surface wet, too. This prevents the paper from clogging. I'm using a spray bottle filled with water and a small amount of car-wash soap to make the surface a little more slippery. Start with 1,000-grit and work down to 2,000-grit. As with block-sanding, when the surface is uniformly dull, you are finished.