[Context and Motivation] User stories are a popular notation for representing requirements, especially in agile development. Although they represent a cornerstone for developing systems, limited research exists on how user stories are refined into conceptual design. [Question/Problem] We study the process of deriving conceptual models from user stories, which is at the basis of information systems development. We focus our attention on the derivation of a holistic view of structural and interaction aspects, represented via class diagrams and use case diagrams, respectively. In this paper, we examine whether providing guidelines has an effect on the ability of humans to derive complete and valid conceptual models. [Principal Ideas/Results] We design example-based guidelines for the derivation of class and use case diagrams from user stories. Then, we conduct a two-factor, two-treatment controlled experiment with 77 undergraduate students serving as subjects. The results indicate that the guidelines improve the completeness and validity of the conceptual models in cases of medium complexity, although the subjects were neutral on the usefulness of the guidelines. [Contribution] The guidelines may assist analysts in the refinement of user stories. Our initial evidence, besides showing how the guidelines can help junior analysts derive high-quality conceptual models, opens the doors for further studies on the refinement of user stories, and to the investigation of alternative guidelines.