Here are a few very useful tutorials on industrial design sketching. Well illustrated and notated threads from the huge resource site Core77. I always enjoy seeing peoples processes in their chosen field, finding out how they arrived at the final product and seeing the development steps in between. Another phenomenal site is ID Sketching that covers topics more specific to technical drawing.



Sketchbook Pro Demo: http://boards.core77.com/viewtopic.php?t=15811
Footwear Photoshop Rendering Tutorial: http://boards.core77.com/viewtopic.php?t=11899
Verithin and Marker Tutorial: http://boards.core77.com/viewtopic.php?t=13739
Quick Concept Sketching: http://boards.core77.com/viewtopic.php?t=4880