Shading is not the easiest thing in the world. Here are a few ways you can improve. Start with a 2d square. And decide where the source of light will be coming from. Say it is coming from the top of the square. Divide the square into 3 sections. The farther away the section is from the source of light the darker it will be shaded in.
Inspiration: Zyra Banez(Youtube)
Thanks for reading,