Pen shading is a thing that you learn with time, practice, and experience. It's got more to accomplish with how you see an object and what concept of it you want to draw. Some time ago, I made a decision to exercise my sketching by drawing in my sketchbook https://ink-drawing-for-beginners82470.creacionblog.com/37100497/5-simple-statements-about-ink-drawing-for-beginners-explained