Instructions for putting things together or understanding how things work are notoriously frustrating. Performance relies on constructing mental models of the object and the actions of the object from text or diagrams or both. Here, we show that instructions can be improved by turning users into designers and deriving design principles from their designs. People first assembled an object and then crafted assembly instructions, using text alone or text and diagrams. Some were required to be brief and to include only the most essential information. Users’ instructions had a narrative structure with an introduction, a middle, and an end. The essential middle described or depicted the step-by-step sequence of actions on parts. Diagrams were regarded as fundamental, and redundancy of depictions and descriptions desirable. These design principles have wide applicability to many kinds of explanations.