Concept art, or concept design, or visual development, is a tool that developers employ to communicate ideas effectively. Matt Rhodes has a fantastic talk about all the ins and outs of concept art for Dragon Age and Mass Effect for BioWare. This really covers most of it.
Matt Rhodes Artist Talk: The World of Concept Art (November 2016)
Neil Blevins also has a fantastic page full of art lessons on his website:
Horia Dociu also has a great talk at GDC where he goes over all kinds of art fundamentals in a fun way.
Concept art is never art for art’s sake. The word art itself is misleading. More applicable is the word craft, as in craftsmanship. Concept artists are masters of their craft. They are more concerned with solving problems than expressing themselves.
Line art is one of the most used drawing processes because it follows so natural from drawing. With line we can indicate a lot of details that would otherwise take many more hours rendering. Line weight is an important subset of line art that is crucial to making good line drawings.
how to think about line weight
Scott Robertson
Matt Rhodes
Sang Nguyen
Danny Gardner
Shape carving is all about working with 1 to two 2 values to establish silhouette and shape. It is usually shown with characters but also works for environments.
Improve Your Designs with Shadow Shapes!
Scott Flanders
Robh Ruppel