How to draw or how to render?

Hey everyone, looking for recommendations on which instructional artbook to get. It's for my boyfriend. He asked for books about drawing backgrounds and constructive drawing, by which he meant drawing without references. He also said he has the basics of perspective, but it might be good to get a refresher.

He can already draw quite well, but I guess they tend to be more 2D/cartoonish style drawings (which is what he prefers). Does anyone have any tips/advice for what to buy?