Some sketching drawing tips
Sketching and Rendering Videos from D Greenwood
https://www.youtube.com/playlist?list=PLac47Xzi2DZ6pP9PpOyvh4vCP_AVuA7ka
https://www.youtube.com/playlist?list=PLac47Xzi2DZ6K0MmYSWQc6Z5l3VaK061c
Product Design Student Series