Thank you for the opportunity to help you with your question!
First you need to practice on viewing light and shadows. Then appreciate the importance of drawing shadows and light ,together with their applications , e.g changing shadows can change a circle into a sphere ,or 2 dimension objects into three dimensions.
Then strive to master the following:
1. Reflected shadows and light.
2. Source of light
3.Dark values in the shadow
4. Highlighting the highlight.
5. techniques of hatching and crosshatching.
With time you will be perfect!
Please let me know if you need any clarification. I'm always happy to answer your questions.