Make sure the paintwork is cleaned well before any polishing takes place. If this is not done then grit, rust and dirt can get worked into the paint. Use standard cleaning equipment and remove any rust with wire wool. Allow it to dry naturally before starting the polishing process.
Dip wet and dry sandpaper into warm water. Allow the drips to stop and go over the surface removing any lumps or imperfections. Continue this process until the paint is smoothed out then wash the surface with some clean water to remove any dust or grit.
Use a foam buffer on a low setting to buff the paintwork to a shiny finish. An automatic foam buffer is best for this as it will bring out the shine without damaging the surface which can lead to rusting in a short space of time. Make sure the buffer is not on too high of a setting. If the buffer is running too fast, the surface can heat up and melt the paint leading to more imperfections.
This form of enamel polishing is good for minor imperfections in the surface, but for very badly faded or chipped paint the only way forward is to repaint the entire surface. If the surface is not repainted, the imperfections may lead to rapid corrosion.