Check out a great guide by Jama Jurabaev.

This Blender guide discusses a creative workflow with Grease Pencil in Blender and Photoshop that will let you create environments, characters, and vehicles. 

You will start with a simple flat sketch and then convert it into a 3D drawing that will "help you with perspective without actually spending a lot of time on tedious 3D modeling.” 

Topics covered:

• Grease Pencil Drawing Technique
• Creating a 3D character design from a 2D flat sketch 
• Vehicle design using mirror modifier
• Environment design using instancing and randomizer

You can learn more and get the guide for $19+ here.