Here's a video on Proko's channel on shading that you might find helpful. https://www.youtube.com/watch?v=-dqGkHWC5IU&t=592s One important thing he often says about shading is that your lightest dark is darker than your darkest light, so it's important to first group your values into the shadows and highlights. Think first about the major planes and forms with shading before getting into the shading of specific places. I think you could maybe benefit from using more gradients on the edges of your shadows. Keep up the good work!