Rami Sayar gave a presentation on data visualization principles and best practices. He covered five principles: 1) context is king, 2) visualizations must match the underlying data, 3) escaping flatland when useful, 4) aggregating details can reveal knowledge in data, and 5) layering and parallelizing views but avoiding "haystacks". He provided examples from Mike Bostock's work with stop-and-frisk data and choropleth maps. Sayar also demonstrated techniques like cubism and recommended resources like books by Edward Tufte and websites like FlowingData.com for learning more about data visualization design.