In my experience, the skill you're talking about is "design". Not design in the sense of graphic design, but design in the sense of identifying the large overarching problem you're attempting to solve through the design of a given thing - a character, a prop, a vehicle, a space, etc. - and breaking it down into smaller problems (especially through the identification of those smaller problems), and ultimately using the tools at your disposal to solve it. Those tools can range from your "visual" library (a collection of visual and/or spatial information pertaining to the various objects and things you've studied from what kinds of hinges exist to achieve different kinds of mechanical motion, to motifs and patterns employed by certain cultures), to a particular combination of shapes, proportions, etc. usually referred to as shape or form language.

Each of these things can be practiced or developed. For getting used to the idea of viewing design as problem solving, give this video a watch. It's a preview for a larger course, but for the purposes of what I've explained here, the video is sufficient and the rest of the course talks about other related things. For developing your visual library, doing drawing/painting studies of a wide variety of things is the best way to absorb and process things in a way that will actually help you retain bits and pieces that you'll be able to pull out later. And the matters of form/shape language and proportion comes down to much the same (studying how other people leverage shape/proportion/etc in their own work) and experimenting with its application in your own work.