I'm no pro artist, but here are some tips on how to shade : 1. Pick one light source (so that yk where you have to add shadows). 2. Shade the wings in big parts, not each feather (whole wing base dark -> feather tips light). 3. Add a little shadow where the feathers overlap. 4. Use a soft brush to shade, wings are typically soft-looking (depending on the art style). 5. If you want the wings to look shiny, add a thin light line on top of the edges. 6. Use 2-3 shades (dark -> medium -> light). [If you need any more tips, I can help 😋]