Have a look at a bundle by Jama Jurabaev that will help you master Grease Pencil in Blender.
The set includes the artist's four top-selling grease pencil tutorials focusing on various creative techniques in Blender.
You'll get over 10 hours of narrated videos explaining techniques for creating environments, characters, creatures and 360 drawings using the grease pencil feature.
The author is a professional art-director / concept artist working in the film industry. He worked on Star Wars, Jurassic World 2, Ready Player One, and many other projects.
You can learn more and get the pack for $50 here.