A broad overview of the best practices involved in designing data visualisations, with heaps of additional context and excellent imagery to really drive home the issues and better solutions. The key list are as follows:

• Don't rely on colour to explain the data
• Don't use very bright or low-contrast colors
• Don't hide important data behind interactions
• Don't overwhelm the user with information
• Do use accessibility tools when designing
• Do use patterns and shapes in addition to colour
• Do use labels and legends
• Do translate the data into clear language
• Do provide context and explain the visualisation
• Do focus on accessibility during user interviews

On the issue with tooltips:

Don't rely on hover effects for explanations. This won't work well on mobile (especially if clicking on a data point already has another action tied to it), and also makes it less accessible for people who rely on screen readers or have mobility issues.