I like to airbrush a mix of gray wash thinned so much that the first coat is hardly noticable. Study the photos of your subject and weather those areas that are faded and dirty. The best models of German WW-2 aircraft I’ve seen tend to show weathering and fading but always leave the white areas, spinners, numbers, crosses, as pure white as the day they left the factory.

For scratches I like to use a metallic base and while the main coat of paint is still drying take a sharp scalpal (#11 blade) and start gently scratching. Time consuming, but injoyable.