I find shading to be the most difficult part of drawing
Hi! Welcome to the community!
Great work. Shading is indeed one of the most difficult parts of drawing, it can make or break an illustration.
One way to do shading, is to imagine a spot where the light comes from and then draw lines from it, that way you can clearly know where it should be shaded and where not, of course, that might ruin your drawing while using traditional tools, but is a great exercise to get the hang of how light behaves.