This proposal focuses on a critical, but often neglected skill for business, communication, and engineering students namely visual literacy, or the ability to assess abstract visual representations of information and knowledge, to evaluate their advantages and disadvantages, to improve their shortcomings, to use them to create and communicate knowledge, or to devise new ways of representing insights. As students starting a course in communication, strategy, informatics, engineering or knowledge management often have diverging prior skills and experiences in visualization, an online leveling course is needed. The faculties of Communication Sciences and Informatics of the University of Lugano will collaborate with the University of St. Gallen and the University of Applied Sciences North-Western Switzerland to develop an online tutorial in English on visualization principles and methods and their applications. The didactic approach consists of rooting visualization in its application contexts, giving students the necessary critical attitude, principles, tools and feedback to develop their own high-quality visualization formats for specific problems (problem-based learning). The students thus learn about the commonalities of good visualization in diverse areas, but also explore the specificities of visualization in their field of specialization (through real-life case studies). They will not only learn by doing, but in doing so contribute new didactic training material for their peers to evaluate. Peer learning is thus an important didactic element of this proposal. The tutorial consists of three building blocks: basic modules, application modules, and exploration modules. The basic modules motivate students for the topic and enable them to understand visualization rules and conventions. The application modules show how these principles can be used for specific communication, engineering, or business problems. The exploration modules let students develop their own solutions and assess each others approaches critically.