Excellent video on how to sand your foil wings. Original is in French but you can use captions and autotranslate (use settings to choose autotranslate into English). If you have some light scratches, you can use an enamel clearcoat or black sanding primary before hand to fill slight scratches, etc. When I'm not lazy, I'll find some of the other posts which talk about filling bigger dings, etc. and link them.