As part of a design-based research effort into disrupting the spread of COVID-19 misinformation, we have iteratively designed, developed, and evaluated a learning intervention intended for public audiences. In this paper we describe the design principles we created to guide our applied research into education on the topic of online misinformation. The six principles guiding our design are: microlearning; equity; relevance and appeal to learners; interventions that do not inadvertently spread misinformation; effective counter messaging; and engagement on an emotional level. These principles are grounded on equitable design, anti-misinformation design, and emotional design.